High idle speed and no more surging after intake rebuild

[82DMC12]

Over the last couple of weeks I've been cleaning up and restoring my intake system including the throttle body, W pipe, and air meter unit. Basically went down to the valley and rebuilt from the bottom up. I have everything re-installed and now I have a high idle.

Symptoms include:


No surging when cold anymore
Idle is starting around 950 and creeping to 1200 by the time the fans come on
If I unplug the idle speed motor plug, the engine doesn't die, in fact nothing happens. I thought the motor should die at idle if the plug is removed? This seems to suggest to me that the throttle isn't closed or there is a vacuum leak
If I manually rev the engine by standing behind the car and turning either the throttle spool, or disconnecting the linkage and pulling back on the arm connected to the throttle, it doesn't always return to the idle speed it was previously at. Sometimes I have to press the arm into the throttle stop to get it to go that last millimeter. It seems like the butterfly plates are sort of hanging up? I have tried disconnecting the linkage to confirm it's not binding and it doesn't improve the situation.


One question I have is, should the butterfly plates close 100% so that they are perpendicular in the throttle? Mine are open a few degrees and if you try to turn them a bit further to perpendicular, it feels like it's binding somewhere (this is even if the arm and spring are removed from the throttle and I'm just turning the threaded end).

I have attempted three times to set the idle by backing out the stop screw and idle switch screw and just barely screwing it in until it hits the stop bracket but I'm not returning to that low 750 RPM like I used to. I'm just stuck at 1000 or greater, and sometimes when revving the engine it gets stuck even higher until I push on the throttle arm to get it to close that last millimeter because the spring on the throttle isn't quite strong enough.

I did a lot of cleaning with carb cleaner, etc in the throttle. The decel springs appear to be in good shape and I did confirm they are fully seated closed the last time I pulled the W-pipe off tonight. New o-rings on the W pipe and new white plastic spacers in front of them. New paper gaskets on the W-pipe and everything is confirmed tight. I have gone over all vacuum lines and vacuum leak areas and can't find anything however I haven't tried spraying starting fluid or anything around yet to see if it would get sucked in.

I guess first thing is to figure out why the Idle speed motor won't kill the engine when I unplug it, and if the butterfly plates are supposed to be truly perpendicular?

[DrWin]

One question I have is, should the butterfly plates close 100% so that they are perpendicular in the throttle? Mine are open a few degrees and if you try to turn them a bit further to perpendicular, it feels like it's binding somewhere (this is even if the arm and spring are removed from the throttle and I'm just turning the threaded end).

For what it is worth, this is what my butterfly plates looks like closed: (I am doing a VOD dive too at this time.)
I don't know if this is how it's supposed to be, when mounted on the engine, but I think mine looks like they close all the way. (When not in the engine.)
67860

[Bitsyncmaster]

The throttle plates should not have to jamb shut all the way. If they do it tends to make them stick closed. I found greasing the throttle return spring on the throttle body is very helpful getting the throttle to return to normal closed. I bet this is your problem since you said you cleaned those parts. You can also increase the spool spring pressure if it is not already in the last notch.

You probably should check your dwell again since any work on the intake can change the setting.

[82DMC12]

For what it is worth, this is what my butterfly plates looks like closed: (I am doing a VOD dive too at this time.)
I don't know if this is how it's supposed to be, when mounted on the engine, but I think mine looks like they close all the way. (When not in the engine.)
67860

Thanks for that. Judging by your photo. I'd say mine are at the same not-quite-perpendicular angle in the rest position.

67864

[82DMC12]

The throttle plates should not have to jamb shut all the way. If they do it tends to make them stick closed. I found greasing the throttle return spring on the throttle body is very helpful getting the throttle to return to normal closed. I bet this is your problem since you said you cleaned those parts. You can also increase the spool spring pressure if it is not already in the last notch.

You probably should check your dwell again since any work on the intake can change the setting.

Thanks Dave. Yes I had really cleaned all the springs with shop towels to get the grime out but didn't add extra grease again. This morning I removed the throttle from the car, removed the arm and spring, and sprayed some silicone lube into the shaft area, working the spindle back and forth and it feels very smooth. Then I put a thick coating of grease on the nub the spring fits over as well as inside and outside the spring. Did the same for the two springs on the throttle spool. The throttle spool is on the second spring stop already. I can't grease it any more! LOL

Last night I did set the dwell even at the higher idle so that I'm not dying from gas fumes.... so the CO is actually quite close right now.

I didn't have time this morning to check the idle after the grease job.... had to go to work. Might be able to try again after work today.

I'm still concerned about the idle motor. I am positive that the idle motor used to kill my engine if I was at idle and I unplugged it. I tried it three or four times yesterday while the engine was idling high and it made no difference, like zero change. I turned the car off and put the ignition in Run (second position) and the idle motor is humming/vibrating. Maybe I will try some of the test procedures found here http://dmctalk.org/showthread.php?11871-idle-air-control-test-procedure

I think if the idle air valve is hanging up or stuck too car open, that would have the same effect as the throttle being cracked open. Is that right?

[CFI]

Thanks Dave. Yes I had really cleaned all the springs with shop towels to get the grime out but didn't add extra grease again. This morning I removed the throttle from the car, removed the arm and spring, and sprayed some silicone lube into the shaft area, working the spindle back and forth and it feels very smooth. Then I put a thick coating of grease on the nub the spring fits over as well as inside and outside the spring. Did the same for the two springs on the throttle spool. The throttle spool is on the second spring stop already. I can't grease it any more! LOL

Last night I did set the dwell even at the higher idle so that I'm not dying from gas fumes.... so the CO is actually quite close right now.

I didn't have time this morning to check the idle after the grease job.... had to go to work. Might be able to try again after work today.

I'm still concerned about the idle motor. I am positive that the idle motor used to kill my engine if I was at idle and I unplugged it. I tried it three or four times yesterday while the engine was idling high and it made no difference, like zero change. I turned the car off and put the ignition in Run (second position) and the idle motor is humming/vibrating. Maybe I will try some of the test procedures found here http://dmctalk.org/showthread.php?11871-idle-air-control-test-procedure

I think if the idle air valve is hanging up or stuck too car open, that would have the same effect as the throttle being cracked open. Is that right?

I’ve unplugged my IAC valve several times and it never stopped the engine. IIRC it helps keep the engine going under different loads (AC on for example) but will not starve the engine of air if it closes completely.

[82DMC12]

I’ve unplugged my IAC valve several times and it never stopped the engine. IIRC it helps keep the engine going under different loads (AC on for example) but will not starve the engine of air if it closes completely.

Well now you have me confused, Perhaps that's not an accurate test. If you pull the IAC motor connector, does the motor close or does it stay in the position it was previously in? I thought it closed, choked off the air, and killed the engine. I could be wrong. I haven't had to deal with idle issues in a very long time so I'm having to relearn some of this stuff.

[Bitsyncmaster]

Well now you have me confused, Perhaps that's not an accurate test. If you pull the IAC motor connector, does the motor close or does it stay in the position it was previously in? I thought it closed, choked off the air, and killed the engine. I could be wrong. I haven't had to deal with idle issues in a very long time so I'm having to relearn some of this stuff.

There is no spring action in the idle motor. So when you pull power it should stay put but vacuum forces and engine vibration may change the position. If you happen to pull the connector slowly or at an angle then that may power one way open or closed.

[82DMC12]

There is no spring action in the idle motor. So when you pull power it should stay put but vacuum forces and engine vibration may change the position. If you happen to pull the connector slowly or at an angle then that may power one way open or closed.

OK so let me ask this. I want to make sure I'm not chasing two problems at once. The first thing I noticed on starting the car, in my cold garage, is the idle did not do the "hunt" it normally does when stone cold with low ambient temp. I'm originally from North Dakota and now living in Kansas where it can easily be 10F to 40F during the day at this time year. For 20 years, my car has had the regular surging hunt when the engine is COLD, like below 40F for sure. I would turn the key, it would crank a couple times, start, and then rhythmically rev to maybe 1100, fall back down to around 750, rev again, fall back down, etc in a very regular pattern until apparently something warms up and the amount of rev diminishes for next two or three revs (like maybe only to 1000, then only to 900, then to 800, then settle in) until the rev meets the idle speed of 750 RPM. Then I have always had a very stable idle. This hunt doesn't happen on a hot or warm engine and doesn't happen at all on a cold engine on a hot summer day. Only cold engine with cold ambient.

I find posts on here from fairly knowledgeable people saying the engine should never hunt, and if it does, that means you have a vacuum leak. Then I find other smart people saying yes actually it does, and if it doesn't, your lambda or IAC isn't working right. I thought this cold hunt was normal and characteristic of DeLoreans with an intact lambda and IAC system.

If it's NOT normal, I need to know that so that I don't go looking for why it's not hunting if it's not supposed to anyway.

[CFI]

OK so let me ask this. I want to make sure I'm not chasing two problems at once. The first thing I noticed on starting the car, in my cold garage, is the idle did not do the "hunt" it normally does when stone cold with low ambient temp. I'm originally from North Dakota and now living in Kansas where it can easily be 10F to 40F during the day at this time year. For 20 years, my car has had the regular surging hunt when the engine is COLD, like below 40F for sure. I would turn the key, it would crank a couple times, start, and then rhythmically rev to maybe 1100, fall back down to around 750, rev again, fall back down, etc in a very regular pattern until apparently something warms up and the amount of rev diminishes for next two or three revs (like maybe only to 1000, then only to 900, then to 800, then settle in) until the rev meets the idle speed of 750 RPM. Then I have always had a very stable idle. This hunt doesn't happen on a hot or warm engine and doesn't happen at all on a cold engine on a hot summer day. Only cold engine with cold ambient.

I find posts on here from fairly knowledgeable people saying the engine should never hunt, and if it does, that means you have a vacuum leak. Then I find other smart people saying yes actually it does, and if it doesn't, your lambda or IAC isn't working right. I thought this cold hunt was normal and characteristic of DeLoreans with an intact lambda and IAC system.

If it's NOT normal, I need to know that so that I don't go looking for why it's not hunting if it's not supposed to anyway.

If everything is working correctly it shouldn’t hunt. Not much anyway. The problem is idle hunting is so common and can happen for so many reasons that most people just live with it.

[82DMC12]

OK I am going to try to forget about the idle hunt because maybe I have fixed so much stuff that my hunt will actually go away.

In the shop manual, it says the thermistor in the Y-pipe will provide for a faster idle if the coolant temp is below 59F. However that faster idle value is not given. The shop manual only describes that idle speed to generally be 775 +/- 50 RPM.

What should I expect as an idle speed in very cold conditions? I suppose this speed will not last long since it doesn't take too long to heat up the coolant.

[Bitsyncmaster]

OK I am going to try to forget about the idle hunt because maybe I have fixed so much stuff that my hunt will actually go away.

In the shop manual, it says the thermistor in the Y-pipe will provide for a faster idle if the coolant temp is below 59F. However that faster idle value is not given. The shop manual only describes that idle speed to generally be 775 +/- 50 RPM.

What should I expect as an idle speed in very cold conditions? I suppose this speed will not last long since it doesn't take too long to heat up the coolant.

If your engine hunts right away on a cold engine than probably the idle motor is sticking cold.

My car will hunt for a minuet or two right after the engine warms up enough to start the lambda running closed loop. What causes that is the lambda turning on before the O2 sensor is really warmed up enough. After that it never hunts. When I was running a wideband unit (heated O2) I never had hunt ever.

The stock idle ECU has one set idle speed (775 RPM). When cold the ECU just limits how much the idle motor can close hence causing a faster idle depending on a lot of other adjustments in the engine. When I was running the stock idle ECU I never saw any fast idle even down to 0 deg.F.

[82DMC12]

If your engine hunts right away on a cold engine than probably the idle motor is sticking cold.

My car will hunt for a minuet or two right after the engine warms up enough to start the lambda running closed loop. What causes that is the lambda turning on before the O2 sensor is really warmed up enough. After that it never hunts. When I was running a wideband unit (heated O2) I never had hunt ever.

The stock idle ECU has one set idle speed (775 RPM). When cold the ECU just limits how much the idle motor can close hence causing a faster idle depending on a lot of other adjustments in the engine. When I was running the stock idle ECU I never saw any fast idle even down to 0 deg.F.

Thanks Dave. Unfortunately we got a cold front and it's far too cold to be standing in the garage with the door open messing with idle. So, I'm just doing some basic checks for now. So far I have:

1) Confirmed the motor will clack to each side with 12V applied to the middle connector and then a ground applied briefly to each outer pin.
2) Sprayed some WD40 into the motor
3) Checked ohms on the pins - I'm getting 10 ohm between the left outer and inner, 10 ohm between the right outer and inner, and 20 ohm between the two outer pins. I found a thread that said I should be reading about double those numbers. Can anyone confirm?
4) Cleaning the contacts
5) Plugged in the IAC but it's disconnected from the in/out hoses. Turned the key to RUN and observed the motor is opening and then slowly closing over the next 30 seconds or so. Seems to be OK.

So my ohms are maybe low if the other thread is to be trusted.

2 more questions as I check stuff -

1) Any advice as to how tight to make the throttle cable going around the throttle spool? My first thought was to make it tight so that the throttle is snappy but I'm thinking that can be preventing it from returning to a closed position. I might try just smartly wrapping the cable around without trying to take all the slack out.

2) Advice on setting the length of the linkage between the throttle spool and the arm? Again, my thought was to remove all slack but that might also be working against me. Maybe it's better to a bit of slop so that the three parts can't risk binding.

[82DMC12]

Thanks Dave. Unfortunately we got a cold front and it's far too cold to be standing in the garage with the door open messing with idle. So, I'm just doing some basic checks for now. So far I have:

1) Confirmed the motor will clack to each side with 12V applied to the middle connector and then a ground applied briefly to each outer pin.
2) Sprayed some WD40 into the motor
3) Checked ohms on the pins - I'm getting 10 ohm between the left outer and inner, 10 ohm between the right outer and inner, and 20 ohm between the two outer pins. I found a thread that said I should be reading about double those numbers. Can anyone confirm?
4) Cleaning the contacts
5) Plugged in the IAC but it's disconnected from the in/out hoses. Turned the key to RUN and observed the motor is opening and then slowly closing over the next 30 seconds or so. Seems to be OK.

So my ohms are maybe low if the other thread is to be trusted.

2 more questions as I check stuff -

1) Any advice as to how tight to make the throttle cable going around the throttle spool? My first thought was to make it tight so that the throttle is snappy but I'm thinking that can be preventing it from returning to a closed position. I might try just smartly wrapping the cable around without trying to take all the slack out.

2) Advice on setting the length of the linkage between the throttle spool and the arm? Again, my thought was to remove all slack but that might also be working against me. Maybe it's better to a bit of slop so that the three parts can't risk binding.

All right, this problem is really kicking my butt. This weekend I pulled the intake manifold off again to very carefully rebuild everything from the bottom up starting with the six o-rings. Everything is spotless and this time I re-assembled with red rubber grease on the o-rings to make sure they aren't slipping around. I'm very confident I have zero vacuum leaks to the outside at this point in time. I'm to the point now where this is my list of symptoms:

1) Idle is starting at about 900 on a cold engine, dwell starts at 22 on 8 cyl scale which confirms open loop
2) Within a few minutes, idle starts to very slowly creep up, around this time we go to closed loop and I'm swinging back and forth over 20 deg, as expected, in closed loop
3) By the time the fans kick on, I'm at 1,400 RPM and I haven't touched the throttle. The engine sounds good and isn't missing or anything. Timing confirmed at exactly 13 deg.

I adjusted the throttle as explained in post #3 of this thread - http://dmctalk.org/showthread.php?722-Backpressure-on-throttle-lever-at-idle

Now I have zero play in the linkage when my throttle spool is fully relaxed/ on the stop so my linkage is helping to push the arm into a closed position. There is no further play in the arm, so I can't make the throttle close any further by pressing on the arm (throttle is not hanging up).

Three air screws in throttle body are all closed. If I unplug the inner harness from the idle ECU, my RPMs go up to about 2,600, and drop back down to wherever they were before once I plug it back in.

This is very strange since I used to sit at 750 when warm and never had any throttle or linkage problems previously. During this rebuild, I painted the throttle body and ended up sanding the paint off where the throttle arm and spring goes just to make sure that wasn't causing it to bind.

My decel springs look normal and don't look "collapsed" or crushed like I've seen photos of bad decel springs. However I did do a lot of cleaning of the butterfly plates including the springs so maybe I somehow weakened them?

Is there any other test I can do short of replacing my throttle body?

[Bitsyncmaster]

Try pulling the vacuum advance hose going to the ignition distributor and see if that reduces the idle RPM.

Keep backing out that curb idle screw.

RPM will increase because the oil gets thinner as it warms up. So if the idle system is not working that would be the result. Does your idle motor hum (vibrate)?

[82DMC12]

Try pulling the vacuum advance hose going to the ignition distributor and see if that reduces the idle RPM.

Keep backing out that curb idle screw.

RPM will increase because the oil gets thinner as it warms up. So if the idle system is not working that would be the result. Does your idle motor hum (vibrate)?

I'll check the vacuum advance hose. I know I'm NOT getting vacuum advance at cold idle because I double-checked it while setting timing yesterday morning.

Will have to keep checking the curb idle screw but if I let it out any further I start to get that stickiness in the butterfly plates where they start to contact the inside of the throttle body. I have it adjust just a hair open so there is no stickiness when operating the arm manually. I followed that other dmctalk post I referenced in the above post which supposedly is a good way to set it. But I don't know.

My idle motor hums with key in RUN position. I applied +12 to the center pin and gounded either side pin and it snaps into place. I also see that when I turn the key to RUN, the motor opens and then slowly closes over the next 30 seconds or so. I have about 10 ohms between left pin and center pin, 10 ohms between right pin and center pin, and 20 ohms between outer pins with the motor removed the car. I cannot really tell if the motor is humming while the engine is running due to other vibrations. Is there anything else I can check on the ISM, or is that pretty definitive that it's working?

[Bitsyncmaster]

I'll check the vacuum advance hose. I know I'm NOT getting vacuum advance at cold idle because I double-checked it while setting timing yesterday morning.

Will have to keep checking the curb idle screw but if I let it out any further I start to get that stickiness in the butterfly plates where they start to contact the inside of the throttle body. I have it adjust just a hair open so there is no stickiness when operating the arm manually. I followed that other dmctalk post I referenced in the above post which supposedly is a good way to set it. But I don't know.

My idle motor hums with key in RUN position. I applied +12 to the center pin and gounded either side pin and it snaps into place. I also see that when I turn the key to RUN, the motor opens and then slowly closes over the next 30 seconds or so. I have about 10 ohms between left pin and center pin, 10 ohms between right pin and center pin, and 20 ohms between outer pins with the motor removed the car. I cannot really tell if the motor is humming while the engine is running due to other vibrations. Is there anything else I can check on the ISM, or is that pretty definitive that it's working?

I've not seen bad deceleration springs that don't look bad but maybe that is your problem. Can you press on the springs to make sure they have some tension? But since the problem came on suddenly that probably is not the problem.

[82DMC12]

I've not seen bad deceleration springs that don't look bad but maybe that is your problem. Can you press on the springs to make sure they have some tension? But since the problem came on suddenly that probably is not the problem.

Here's a picture of my decel springs. I can squeeze them and they move freely. The plate that gets sucked open by vacuum on each butterfly is fully seated on both sides. Hard to imagine this would be my problem unless it's possible for the springs to crap out without collapsing. Not sure how to measure that.

67942

[Bitsyncmaster]

The springs look good.

[82DMC12]

I worked on this some more last night and can report the following:

1) There is no ignition advance at idle either hot or cold, confirmed by pulling the hose off the advance
2) I put my K-Jet gauge on this time while idling to make sure my control pressure is not going wild at the request of another owner - confirmed my control pressure starts at 1.8 bar (55F in my garage) and maxes out at 3.4 bar
3) Confirmed my idle switch is indeed closed and detected closed at the idle ECU by checking voltage between battery and black/green on the inner ECU plug
4) Confirmed the following readings from my thermistor at the ECU plug - when cold, 13.3 on the 20K scale, and when hot, 2.35 on the 20K scale.
5) Also tried jumping out the thermistor at the white church window plug by jumping black/slate and black/yellow. This made no difference.
6) Tried resetting idle screws one more time while the engine is hot - it dropped slightly but still elevated. Even by pushing on the throttle arm with the curb idle backed out, and ECU screw screwed in, it won't idle at 775.

Somehow it just keeps raising as it gets hot to about 1,300 RPM.

Is it possible the idle ECU is flaking out?

[Bitsyncmaster]

Is it possible the idle ECU is flaking out?

It's possible but usually ECU failures are the driver transistors from a shorted idle motor. But your running out of things to check so if you can get another owner who will let you borrow his ECU than that would confirm or eliminate that problem.

[MrChocky]

It's possible but usually ECU failures are the driver transistors from a shorted idle motor. But your running out of things to check so if you can get another owner who will let you borrow his ECU than that would confirm or eliminate that problem.

I have one spare. If you end up wanting to send to Dave for upgrade to his, we can work that out.

[82DMC12]

I have one spare. If you end up wanting to send to Dave for upgrade to his, we can work that out.

Thanks! Might end up taking you up on it. I'd appreciate being able to simply borrow it for a day just to swap out and check, if it comes to that. I'm definitely running out of things to check. I don't really want to spend $100+ on a smoke machine I'll probably never use again.

A couple things I could try -

1) Remove the vacuum line from the passenger side of the intake and plug the barb. Maybe there's a vacuum leak upstream from there.
2) Swap Idle ECU for known good ECU
3) Swap throttle body for known good throttle body
4) Keep working on the linkage. I guess I could remove the wires from the idle speed switch and join them, then back out the idle stop screw 100% and just hold the throttle closed. See if that results in the right idle speed. If it does, then I know my problem is related to the butterflies sticking or some kind of weird linkage binding or some crazy thing in the spool that was OK before but now isn't.

[82DMC12]

Thanks! Might end up taking you up on it. I'd appreciate being able to simply borrow it for a day just to swap out and check, if it comes to that. I'm definitely running out of things to check. I don't really want to spend $100+ on a smoke machine I'll probably never use again.

A couple things I could try -

1) Remove the vacuum line from the passenger side of the intake and plug the barb. Maybe there's a vacuum leak upstream from there.
2) Swap Idle ECU for known good ECU
3) Swap throttle body for known good throttle body
4) Keep working on the linkage. I guess I could remove the wires from the idle speed switch and join them, then back out the idle stop screw 100% and just hold the throttle closed. See if that results in the right idle speed. If it does, then I know my problem is related to the butterflies sticking or some kind of weird linkage binding or some crazy thing in the spool that was OK before but now isn't.

Hey everyone,

I don't like leaving threads that I started "open" so I thought I'd provide an update.

1) I was able to confirm my vacuum coming off the passenger side barb is tight - I used a Mityvac to pull a vacuum and it held. I removed the vacuum hose from the driver side barb and did the same - also holding. So I knew I wasn't leaking vacuum through a hose or fitting.

2) Performed enough tests of the Idle ECU to effectively rule it out with 99% certainty

3) Didn't swap the throttle body because I kept working on the linkage. What seemed to help was to disconnect the linkage rod from the throttle spool, back out both idle stop screws (the curb idle screw and the throttle microswitch screw) and push down on the throttle arm so that the throttle was seriously closed while I slowly turned the curb screw back in until it just started to lift. Then I turned the microswitch screw in until the switch engaged and gave it another 3/4 turn. Then, on the rod, I loosened both jamb nuts so that I could turn the rod to lengthen or shorten the rod rather than loosening only the spool-side nut and turning the ball end a complete revolution either way. By turning the rod, I got much finer adjustment available and basically just shortened the rod until I couldn't shorten it anymore with my fingertips while the rod was attached at both ends. That way the spool was holding the throttle closed in rest position.

So now I'm sitting around 850 RPM maximum at hot idle but sometimes it drops to 750. I'm so close and I'll do a bit more tweaking but the linkage really is touchy. At least I was able to go for a nice drive this weekend and enjoy the car - the engine is running super smooth again! Also no more "dieseling" when I shut down.

I also replaced the rubber throttle body spacer with a DPI billet aluminum spacer - it has a larger diameter and doesn't restrict the air flow. Call me nuts but I feel like I have a bit more power in the mid-range now.

If I come up with any more advice I'll be back here to share it.

[David T]

Based on what you just did, your Quadrant Link (the rod that connects the throttle arm to the throttle spool) is worn. The ball ends wear and develop play so when you release the throttle, it doesn't go all the way closed. That rod (link) has left and right hand threads so it can be finely adjusted but once you get wear you can only adjust the play out in one direction. You might notice a slight lack of response when you step on the pedal, that's the play (looseness) you are taking out before you move the throttle arm. There are 3 springs in the throttle linkage. 2 in the throttle spool and one in the throttle body. After 30 + years the grease and oil that was originally in there turns to glue. If you want the throttle to operate smoothly it should all be taken apart, cleaned and relubricated. It also wouldn't hurt to lubricate the throttle cable as per the recall with some anti-freeze. The way I do it, I disconnect the cable at the throttle spool, attach a piece of hose that slips over the end, and secure it with a hose clamp. Fill the hose with anti-freeze and then hook an air line to the end. Pressurize the cable till you see anti-freeze come out the end by the pedal.
For the throttle body, there are 2 set screws. One is the stop for the throttle arm and should not ever need to be adjusted and the other is for the idle switch. Do not over adjust it, it should just trip that micro and not push too far after that. Check that the decel springs are holding the valve plates closed. If the motor ever backfired it fried those springs and they lose the ability to hold those valves shut. Replace them with some springs from retractable pens. Cut them to fit. Vacuum leaks are the bane of trying to get the motor to run and idle correctly. Any leaks take away from the idle motor's ability to control the idle so make sure you have fixed ALL of the vacuum leaks. Best way to find them is with a smoke machine. Some common things that leak are the injector seals and the "O" ring for the air pipe that goes to the idle motor on the bottom of the mixture unit.

[DMC-Ron]

It also wouldn't hurt to lubricate the throttle cable as per the recall with some anti-freeze. The way I do it, I disconnect the cable at the throttle spool, attach a piece of hose that slips over the end, and secure it with a hose clamp. Fill the hose with anti-freeze and then hook an air line to the end. Pressurize the cable till you see anti-freeze come out the end by the pedal.

David,
What are you using for the anti-freeze (anti-seize) lubricant. Could you post a link or provide the name?

Ron

[David T]

David,
What are you using for the anti-freeze (anti-seize) lubricant. Could you post a link or provide the name?

Ron

The good ole green stuff, aka Prestone, mixed 50/50 with water as per the throttle recall.

[DrWin]

So I basically want to ask a related question: Anyone wants to chance a guess as to what is going on with my engine after my VOD rebuild?

Engine cold, ambient temp below <15*C => Engine starts, hunts for 5 secs, goes to 600-700rpms and runs steady for 30 secs. Dwell meter steady at 22* (8-cyl scale).
Engine warm (?), ambient temp < 15*C => Sudden change to 900rpms, runs steady for a few minutes. Dwell meter steady at 22* (8-cyl scale).
Engine warmer (?), ambient < 15*C => Gradually changes up to 1100rpms, runs steady. Dwell meter has started to move between 23* and 17* (8-cyl scale).


My impression is that the change from open to closed loop on the idle speed ECU and the changes in rpms weren't coincidental, that is the timing wasn't a match.
I sounded more like the changes weren't syncronised, like it was several different things that actvated in sequence. (Makes sense?)

Also, I just tested what happens when I hit the gas - It revs up to whatever and then drops down to 775rpm OR stays at 1100 rpms, seemingly at random. This strongly suggests that the throttlecable is sticking, right?

[SS Spoiler]

same problem, idle creeps up as it warms up.
but if I turn my lights on and off it drops to normal.
ideas?....

[David T]

Reread post # 25. Either you have play in the linkage or it is sticking.

[Bitsyncmaster]

same problem, idle creeps up as it warms up.
but if I turn my lights on and off it drops to normal.
ideas?....

Back off your curb idle. If it's all the way backed out then probably you deceleration springs could be bad. Also if you get ignition advance at idle that is another cause. You can test that by pulling the advance hose going to the distributor.

[82DMC12]

same problem, idle creeps up as it warms up.
but if I turn my lights on and off it drops to normal.
ideas?....

Not sure what the lights have to do with it, but I'm OP and I had the same problem with idle slowly creeping up as it warms up. The problem was my linkage rod wasn't short enough to keep the throttle plates 100% closed. I had better luck adjusting it by loosening both lock nuts and turning the rod shorter rather than trying to turn just one end shorter. I was able to make finer adjustments that way. I'm not convinced I have it totally perfect (yet) but that did stop the idle from slowly increasing. I've been swamped with work and a 5-month old boy, plus the weather sucks this spring so far, so I haven't had as much time to tinker as I would like.

[Ron]

So I basically want to ask a related question: Anyone wants to chance a guess as to what is going on with my engine after my VOD rebuild?

Engine cold, ambient temp below <15*C => Engine starts, hunts for 5 secs, goes to 600-700rpms and runs steady for 30 secs. Dwell meter steady at 22* (8-cyl scale).
Engine warm (?), ambient temp < 15*C => Sudden change to 900rpms, runs steady for a few minutes. Dwell meter steady at 22* (8-cyl scale).
Engine warmer (?), ambient < 15*C => Gradually changes up to 1100rpms, runs steady. Dwell meter has started to move between 23* and 17* (8-cyl scale).


My impression is that the change from open to closed loop on the idle speed ECU and the changes in rpms weren't coincidental, that is the timing wasn't a match.
I sounded more like the changes weren't syncronised, like it was several different things that actvated in sequence. (Makes sense?)

Also, I just tested what happens when I hit the gas - It revs up to whatever and then drops down to 775rpm OR stays at 1100 rpms, seemingly at random. This strongly suggests that the throttlecable is sticking, right?For the first part- When it is <15°C, the dwell should be 50-60° = 25-30° on 8-cyl scale, steady. Your's is 3° below the minimum. Given that, 1. and 2. above makes sense. And for 3., it is dead on (swinging about 40° = 20° on 8-cyl scale. You might try adjusting it a tad (richer, iirc), which may bring the cold dwell up and make the warm dwell swing wider (10° instead of 6°, about 20° 8 cyl scale. (...maybe not ;-).

The change at .2 could just be the WUR/CPR changing the control pressure (until it reaches 40°C = 104°F).

For the last part- I agree that the linkage is at least playing a part when it stays at 1000 RPM.

=========

Looks like we are getting too many cars/issues for one thread...

[DrWin]

For the first part- When it is <15°C, the dwell should be 50-60° = 25-30° on 8-cyl scale, steady. Your's is 3° below the minimum. Given that, 1. and 2. above makes sense. And for 3., it is dead on (swinging about 40° = 20° on 8-cyl scale. You might try adjusting it a tad (richer, iirc), which may bring the cold dwell up and make the warm dwell swing wider (10° instead of 6°, about 20° 8 cyl scale. (...maybe not ;-).

The change at .2 could just be the WUR/CPR changing the control pressure (until it reaches 40°C = 104°F).

For the last part- I agree that the linkage is at least playing a part when it stays at 1000 RPM.

=========

Looks like we are getting too many cars/issues for one thread...

Either that or we are getting enough cars for a great discussion/techsession. :)

So - yeah… I looked into the throttle cable/body area and can tell that something is binding somewhere, b/c the throttle doesn’t automatically reset to nil after I release the throttle pedal and/or cable (if pulling from the engine bay).

When I manually push it to nil, rpms drops to 700-750 ish and stays steady (if a little rough).

This also seems to suggest that the idle creep up I was experiencing earlier is because the throttle spool doesn’t rotate far enough back to activate the idle speed microswitch, which causes opening the vacuum advance solenoid, which then goes on to supply vacuum to the distributor (advance). (Right?)

So, I’ll look more into that to figure this out. Is there a “trick” to mounting throttle cable to the clip to the valve cover, from the de-ice recall kit? I kind of suspect that’s where the binding might be?


Sent from my iPhone using Tapatalk Pro

[Bitsyncmaster]

When I first bought my car, I found the throttle cable clamp on the passenger side valve cover had worn through the plastic coating and the that caused the cable inside to rust there and stick.

[Ron]

Either that or we are getting enough cars for a great discussion/techsession. :)

So - yeah… I looked into the throttle cable/body area and can tell that something is binding somewhere, b/c the throttle doesn’t automatically reset to nil after I release the throttle pedal and/or cable (if pulling from the engine bay).

When I manually push it to nil, rpms drops to 700-750 ish and stays steady (if a little rough).

This also seems to suggest that the idle creep up I was experiencing earlier is because the throttle spool doesn’t rotate far enough back to activate the idle speed microswitch, which causes opening the vacuum advance solenoid, which then goes on to supply vacuum to the distributor (advance). (Right?)

So, I’ll look more into that to figure this out. Is there a “trick” to mounting throttle cable to the clip to the valve cover, from the de-ice recall kit? I kind of suspect that’s where the binding might be?


Sent from my iPhone using Tapatalk ProMine was binding like Dave's when I got the car.
But years later, it was the rod joints got too sloppy. Seems I had to adjust it a tiny bit longer so it would push the butterfly/lever shut, instead of shorter as Andy mentioned???

[82DMC12]

Mine was binding like Dave's when I got the car.
But years later, it was the rod joints got too sloppy. Seems I had to adjust it a tiny bit longer so it would push the butterfly/lever shut, instead of shorter as Andy mentioned???

I haven't been in this thread for a while because I've been distracted by a couple other issues. However to address Ron's last question, the rod actually has to be made shorter if you want to take up slack AND pull the throttle arm so that it presses more firmly against the stop plate.

Here's a little update from my car. I'm not sure where things started to go a bit wrong again, but they are. I can start the car cold and it will start at about 775 RPM, but then within a few minutes as things warm up, the idle slowly comes up to around 1,000 - 1,100. This is just letting the car idle without ever touching the throttle. If I goose it while in neutral (manual trans) sometimes the RPM's drop back down to 775 however when it is at 1,000 it is NOT because the throttle is binding, that I am 100% sure of. The throttle is as closed as it can be and the stop screw is as backed out as it can but still take the abuse from the throttle spool snapping back on deceleration.

I DID BUY A SMOKE MACHINE and I have confirmed there are NO vacuum leaks on a cold engine. Last night I ran the car until the fans came on, then shut it down and did another smoke test on the HOT engine - no smoke leaks except a tiny bit from the oil dip stick which probably isn't actually a vacuum leak since the engine would be sucking the stick downward in normal operation. So I think I have completely ruled out vacuum leaks.

I'm really at a loss as to what else to check. I've gone over everything multiple times.

I did pull my spark plugs out this weekend to check them and all of them look like they've been running somewhat hot. Here a couple pictures of them so I'd be glad to get all your opinions. They are NGK 2238 TR5's and only have maybe 250 miles on them. I recently learned that an NGK heat range of 5 is more like an 8 in Bosch-speak so I think they do run hot. I'm replacing them Bosch HR6DC's that I found on ebay (copper instead of OEM silver). I do think my idle is a bit rough so maybe these NGK plugs are not good.

I pulled the distributor out to check the reluctor air gap since I did replace the impulse coil a few months ago but didn't know the gap was a "thing". It's now gapped exactly perfect.

CO has been checked multiple times and everything is in spec.

Timing has been checked multiple times - perfect. Also put a light on each of the six plug wires and they are all flashing consistently so I'm not losing a cylinder here and there.

I checked injectors again by placing them in glass jars and jumping the RPM relay. No drips with a neutral air plate and no drips after pushing down on the plate and releasing it. The spray pattern looks good on all six and the volume is equal after 30 seconds. I'm going to check fuel pressures one more time just to make sure my control pressure isn't F'ing up.

Not too such what else to do unless my idle motor is somehow defective, or my non-collapsed decel springs are too lose to keep the throttle buttons closed when they warm up. I might have to buy a new throttle body and just try that.

68569 68570

[Bitsyncmaster]

Here's a little update from my car. I'm not sure where things started to go a bit wrong again, but they are. I can start the car cold and it will start at about 775 RPM, but then within a few minutes as things warm up, the idle slowly comes up to around 1,000 - 1,100. This is just letting the car idle without ever touching the throttle. If I goose it while in neutral (manual trans) sometimes the RPM's drop back down to 775 however when it is at 1,000 it is NOT because the throttle is binding, that I am 100% sure of. The throttle is as closed as it can be and the stop screw is as backed out as it can but still take the abuse from the throttle spool snapping back on deceleration.


That's what my car did for so many years and it turned out to be bad deceleration springs. So far if you look at the springs and see uneven coils you know it's bad but I wonder if good looking springs can go bad.

My car would idle at a perfect 775 RPM cold and would end up at 1000 RPM warm and I had the curb idle screw fully backed out.

[82DMC12]

That's what my car did for so many years and it turned out to be bad deceleration springs. So far if you look at the springs and see uneven coils you know it's bad but I wonder if good looking springs can go bad.

My car would idle at a perfect 775 RPM cold and would end up at 1000 RPM warm and I had the curb idle screw fully backed out.

I've been avoiding blaming the decel springs because there is no easy fix besides replacing the throttle, and those are hard to find now. I see DPI has a "refurbished" throttle available for about $400 and Ed seems to have a NOS throttle for about $500 USD. Doesn't show available via DMCH website but sometimes there's a solution. I have also avoided blaming the springs because they are not collapsed.

If anyone out there has a known good throttle body I'd be glad to pay shipping both ways if you'd be so kind to loan it out for a test!?!

[Bitsyncmaster]

I've been avoiding blaming the decel springs because there is no easy fix besides replacing the throttle, and those are hard to find now. I see DPI has a "refurbished" throttle available for about $400 and Ed seems to have a NOS throttle for about $500 USD. Doesn't show available via DMCH website but sometimes there's a solution. I have also avoided blaming the springs because they are not collapsed.

If anyone out there has a known good throttle body I'd be glad to pay shipping both ways if you'd be so kind to loan it out for a test!?!

With engine swaps and a lot of EFI the throttle bodies should become more available and priced less. In the past you could find them for less $100. If you can find a way to lock yours down to test, that would also work. Maybe some hot glue.

[David T]

Springs from ball point pens are a good substitute for the decel valves.

[82DMC12]

If you can find a way to lock yours down to test, that would also work. Maybe some hot glue.

That's a VERY good idea - hot glue can be removed easily when I'm done testing. First I am going to replace my spark plugs with NOS Bosch HR6DC (same as OEM but copper instead of silver). I wonder if these NGK's which are running too hot are causing crazy things with poor combustion and the idle system is over compensating. Once the new plugs are in, if the idle is still high, I will glue them shut.

[David T]

Gluing them shut is OK for testing purposes but if it is a 5 speed you should keep them operable. They serve no function on the automatics. Deloreans are unique in that the specs on the motor ( timing, idle speed, vacuum and mechanical advance) are exactly the same no matter 5-speed or auto. You don't see that on most other cars. The idle speed is supposed to go down as the motor warms up, not increase. My guess is there is looseness (play) in the throttle linkage (especially the rod ends of the quadrant link) and that is allowing the motor to speed up as it gets warmer. Disconnect the thermister and see what happens.

[82DMC12]

Gluing them shut is OK for testing purposes but if it is a 5 speed you should keep them operable. They serve no function on the automatics. Deloreans are unique in that the specs on the motor ( timing, idle speed, vacuum and mechanical advance) are exactly the same no matter 5-speed or auto. You don't see that on most other cars. The idle speed is supposed to go down as the motor warms up, not increase. My guess is there is looseness (play) in the throttle linkage (especially the rod ends of the quadrant link) and that is allowing the motor to speed up as it gets warmer. Disconnect the thermister and see what happens.

I already know my thermistor is showing closed circuit when both cold and hot though the values seem to be a bit lower than I see often reported. I'm at about 8,000 ohm cold and 850 ohm hot.

What SHOULD happen if I remove one of the pins from the ECU plug that corresponds to the thermistor? My understanding is open circuit on the thermistor results in a high idle, like 3,000 RPM.

If I wanted to jump the thermistor and close the circuit , would I use a 10K resistor (like about 1 watt) and bridge the two pins on the on the ECU plug? That would simulate a cold engine all the time to the ECU.

Am I thinking this straight?

[Bitsyncmaster]

I already know my thermistor is showing closed circuit when both cold and hot though the values seem to be a bit lower than I see often reported. I'm at about 8,000 ohm cold and 850 ohm hot.

What SHOULD happen if I remove one of the pins from the ECU plug that corresponds to the thermistor? My understanding is open circuit on the thermistor results in a high idle, like 3,000 RPM.

If I wanted to jump the thermistor and close the circuit , would I use a 10K resistor (like about 1 watt) and bridge the two pins on the on the ECU plug? That would simulate a cold engine all the time to the ECU.

Am I thinking this straight? Running the thermistor open will only let the idle motor close very little. Quite a bit from fully closed. It's not a controlled RPM so it dependents on the other engine adjustments. Mine ran about 2500 RPM with an open thermistor. The idle RPM is fixed at 775 RPM not dependent on the engine temp. From memory 5 Kohms or below let the idle motor close to it's minimum. The stock ECU never really closed it fully on my car.

[82DMC12]

Running the thermistor open will only let the idle motor close very little. Quite a bit from fully closed. It's not a controlled RPM so it dependents on the other engine adjustments. Mine ran about 2500 RPM with an open thermistor. The idle RPM is fixed at 775 RPM not dependent on the engine temp. From memory 5 Kohms or below let the idle motor close to it's minimum. The stock ECU never really closed it fully on my car.

Dave, what would happen if I bridged the two thermistor wires at the white ECU connector? Can I do this with a simple wire tinned at both ends, or should I use a 10K resistor that simulates the thermistor?

Andy

[Bitsyncmaster]

Dave, what would happen if I bridged the two thermistor wires at the white ECU connector? Can I do this with a simple wire tinned at both ends, or should I use a 10K resistor that simulates the thermistor?

Andy

Just do a short circuit. The short circuit will do the same as a 5 Kohm resistor.

Now it does adjust the start opening when starting the engine with the stock or my ECU so if you find hard starting you may have to return to the thermistor.

[82DMC12]

Just do a short circuit. The short circuit will do the same as a 5 Kohm resistor.

Now it does adjust the start opening when starting the engine with the stock or my ECU so if you find hard starting you may have to return to the thermistor.

Thanks Dave. I will try it one more time once I get new spark plugs installed (early next week).

[82DMC12]

Hey guys,

I have performed more tests in an attempt to rule out particular components related to the idle speed, particularly the thermistor and the idle speed motor. I believe I have ruled out the thermistor completely, and I have ruled out the idle motor itself however it's still possible there is some kind of interference affecting the signal to it when the engine gets hot.

Here is what I found last night:

First I checked the thermistor's 20K ohm value between Black-yellow and Black-Slate on the "inner" plug of the idle ECU (the one with only four wires on it).

Stone cold engine but hot summer day in my garage - 4.xx on 20K scale (indicating the thermistor is warm enough due to ambient that no "fast idle" is required)

Test 1 - I pulled out the idle motor but left it plugged into the black plug. I turned the key to ON (Position II) and quickly went back to look at the motor with a flashlight. I saw the "gate" inside had opened completely and after a few seconds it began to retract towards the left (as installed). It closed until there was but a small space the thickness of a slotted screwdriver blade remaining for air to go though.

Test 2 - I then turned off the key and removed the black-yellow wire from the white plug (insert a small jeweler screwdriver under the female spade and push up while pulling the wire out to release the lock clip). This resulted in open-circuit and lack of continuity to the thermistor. I repeated the test and found the motor will only close about half way.

Test 3 - I then removed all four wires from the white plug and made a new jumper that connected the terminals that the thermistor goes to on the idle ECU itself, then plugged in the other two wires (black-green and white-slate) being very careful that they were secure and cannot touch. I turned the key to ON and checked the motor - exact same behavior as the first test, closing nearly completely.

I reinstalled the idle motor and then ran the car up to normal operating temperature with the jumper installed. After about 20 minutes of idling my idle started to climb as I have been trying to solve for weeks now (thermistor totally removed from the circuit so now I know the thermistor is not my issue!). I pulled out the motor once again (quite hot by now!) and repeated Test 3 and found the motor closed to the same nearly closed position even though the idle had been about 1,000 RPM and erratic. So I believe I have effectively ruled out the idle motor itself as defective when both cold and hot.

I made a video of my car's condition starting from stone cold start to high idle with erratic tachometer needle. The video is about 7 minutes long but should demonstrate perfectly what I'm trying to solve.

Thoughts????

https://youtu.be/rJJejVVsPk8

[Ron]

FWIW- It seems odd to me that the voltage droped over time, especially since the RPMs rasied too.

...not sure how accurate your gauge is, but it should be reading around 14.2V instead of 13V after all that time...
(May be related to the tach flicker as well??)

[82DMC12]

FWIW- It seems odd to me that the voltage droped over time, especially since the RPMs rasied too.

...not sure how accurate your gauge is, but it should be reading around 14.2V instead of 13V after all that time...
(May be related to the tach flicker as well??)

The gauge reads about 1V low for sure. When I had the binnacle out a couple weeks ago I was going to take the needle off and put it back on a bit higher but it wouldn't budge and I didn't want to break it. I just installed a new DPI alternator two weeks ago so I will double-check the volts when hot at the jump start post next time I'm working on it. The alternator replacement had no effect on this issue, I was really hoping I had something fried in the alternator causing weird voltage but I guess not. The alternator needed work anyway because the bearing was a little noisy (15 year old Hervey unit)

[82DMC12]

Another update -

1) I disconnected the grounds from the RPM relay, the idle speed microswitch, and the idle ECU and ran temporary grounds joined at the battery. I then started the car and it made no improvement in either the idle quality or the bouncing tach gauge so I don't think a have a bad ground. I also cleaned the ground that attaches to the frame under the jump start post.

2) Removed the throttle body from the car and cleaned the butterflys with alcohol prep pads and then put two dabs of hot glue on each decel valve. See picture below. As I was reinstalling the throttle body, I saw my worklamp shine through the butterfly plates and noticed one of the plates was not centered as well as the other. I slightly loosened the split screws just enough to get a bit of play and re-aligned the plate. I then started the car there was no improvement! So, I think I can rule out bad decel springs.

3) I decided to do another smoke test and found similar results as before when I did a smoke test - some leakage around the oil dipstick rubber tip, leakage at the lower crankcase where the dipstick tube fits into the engine, and a new one I didn't have before - a bit of smoke coming out around where the throttle butterfly shaft end comes out of the throttle body. Not too surprising since it seems there is a tiny bit of play in the throttle shaft when everything is out on the bench. I don't know if this is a problem or not, it could just be that as I seal up other places, the smoke is going to find increasingly small places to come out.

So, at this point I'm not sure where to move forward. I feel like I've checked everything that I can without just randomly replacing stuff. If I were to randomly replace stuff, I'd be looking at:



Tachometer dash gauge - I replaced the board but not the face. Apparently there are magnets or some kind of dampening systems on the gauge separate from the circuit board. Maybe something happened to the dampener and that's causing my tach jumping. Totally unrelated to the idle coming up but maybe that would fix one issue? Once again I hooked up my Actron tach to the coil white/slate and checked the RPM's and the external tach isn't jumping around crazy so either the Actron has better dampening or the dampening in the dash gauge is bad. I don't know how else to monitor the white/slate signal unless I had an oscilloscope.
Idle Speed Motor - I cannot come up with any proof that my idle motor is bad because it passes every test, but maybe something is wrong with it
Ignition ECU - Just another place where white/slate goes, maybe something happened to the ECU when I had my Accel Super Stock coil hooked up backwards for the last 20 years.


68623 68624

[Bitsyncmaster]

I was hoping that test of the deceleration valves would solve the problem. Anyway it reinforces that problem shows up when you see bad springs. I can loan you one of my idle ECUs if you pay for shipping both ways. I also have spare ignition and lambda ECUs but don't think that's your problem.

[82DMC12]

I was hoping that test of the deceleration valves would solve the problem. Anyway it reinforces that problem shows up when you see bad springs. I can loan you one of my idle ECUs if you pay for shipping both ways. I also have spare ignition and lambda ECUs but don't think that's your problem.

Thanks Dave, I appreciate that. I actually have a spare idle ECU that I borrowed from someone else but I don't know that it has been confirmed that it works perfectly either! I think the chances of two ecu's having the same weird problem would be very low. However if I look closer at the ignition ECU I might take you up on that.

I think you are right in that the springs have to look bad in order to actually be bad. There's also no way to adjust the tension on the springs unless you melt off the solder on the end caps. I'm not going to do that, I'm just going to leave the springs alone.

I'll probably order a new dash tachometer on Monday so I can at least give that a try.

[82DMC12]

Hey everyone, I think I have some good news.

I pulled my distributor out AGAIN this morning and reinstalled my old impulse coil and put a new "fly tach lead" on - this is the wire that comes off the impulse coil and goes to the plug that sits in the firewall (white and yellow Bosch two-pin plug). After buttoning everything back up and adjusting the throttle one more time, I did not have the jumpy tach OR the elevated idle! I have been working on the car and taking test drives for much of the day and none of my symptoms returned.

So, I cannot say for sure if the tach problem and the higher idle were definitely linked, but the jumpy tach was definitely caused by either a defective NOS impulse coil or my old fly tach lead was just breaking down.