Idle Backwards

[Ricker]

So here is a problem I have had for some time now. When the engine is COLD the engine idles at 775 RPMs. Then when it gets HOT it idles at 1,500 RPMs. So where do I start testing to see what is bad now?

[r00b]

Check if you're idle speed motor is stuck.

[Bitsyncmaster]

Look at your deceleration valve springs. If the springs are not evenly spaced, you have the bad ones most likely.

[Ricker]

Look at your deceleration valve springs. If the springs are not evenly spaced, you have the bad ones most likely.

Well first off, I have no idea where they are located to even check them, dummy me. Second, in trying to find them on the internet, etc., I read that they do nothing fir an automatic transmission. Mine is an automatic. Maybe should have said that in the beginning. Is this correct or should I still be checking?

[Ricker]

Check if you're idle speed motor is stuck.

The car starts at the low 775 RPM and runs kind of rough. Then when it hits a higher temperature, it runs at 1,000 - 1,200 RPM and real smooth. Both times when cold and hot I disconnected the electrical plug from the idle speed motor - no change whatsoever in the RPM. I'm guessing that means it has issues? Checking here because it is such a pain to get out. The microswitch is set to connect when at no foot pedle.

[Bitsyncmaster]

The car starts at the low 775 RPM and runs kind of rough. Then when it hits a higher temperature, it runs at 1,000 - 1,200 RPM and real smooth. Both times when cold and hot I disconnected the electrical plug from the idle speed motor - no change whatsoever in the RPM. I'm guessing that means it has issues? Checking here because it is such a pain to get out. The microswitch is set to connect when at no foot pedle.

I had the same problem. It held 775 RPM until it warmed up and then ran at 1000 RPM even with the curb idle screw backed all the way out. The problem was the deceleration valve springs. I got a replacement throttle body and that cured the problem.

[Michael]

I would first start with basics (especially if this happened recently), before looking at springs in the throttle body which rarely go bad. check to see if the idle circuit is working, or at least energizing. Secondly, check your vacuum lines, especially at ISM, valve cover back where the distributor advance solenoid is and make sure the plug is on.

As far as the idle circuit goes, make sure the microswitch is engaging and check for continuity. Deceleration springs and ISM's can go bad, but it's not common and probably not the cause here. I would suspect a bad idle computer before any of that.

[82DMC12]

I had a similar problem once, after doing a valley rebuild. Turned out the throttle linkage was just not set up quite right. It would do this reliably if I started the engine cold and touched NOTHING... after a few minutes the idle would very slowly start to come up and stick around 1,000 or higher can't remember exactly where but I have a thread on here. I had to disconnect all the linkage and start from square one with all the adjustments. That fixed it.

[glockworks21]

^^^

same. I think Andy actually helped me when I had this problem. I changed throttle spool springs and cleaned up cable. It was sticking. then adjusted the cable on the spool to get the right tension.

[r00b]

The car starts at the low 775 RPM and runs kind of rough. Then when it hits a higher temperature, it runs at 1,000 - 1,200 RPM and real smooth. Both times when cold and hot I disconnected the electrical plug from the idle speed motor - no change whatsoever in the RPM. I'm guessing that means it has issues? Checking here because it is such a pain to get out. The microswitch is set to connect when at no foot pedle.

My engine would start out with a normal RPM and once warmed up it would idle high. It didn't idle rough when first started though. The problem was my idle speed motor. Before it started, could moisture have gotten into the engine? You can take it off and look inside, if the rotating door in the ISM moves smoothly then the problem is probably not the ISM. If it is the problem you can get a replacement on amazon for around $40.

[Ricker]

After all the excellent advice from everybody (and greatly appreciated) on what to look for and reading other threads, here is what I did and found. The microswitch does engage when the throttle is at idle. It has continuity. Next, I checked the ECU. Pulled the center side plug and the RPMs increased and decreased when back installed. Then on to the idle speed motor. It was humming/vibrating with the key on BUT the valve did not open when the key was initially turned on. Therefore, I believe I need a new idle speed motor. Am I missing anything before I buy a new idle speed motor?

[Rich]

Therefore, I believe I need a new idle speed motor. Am I missing anything before I buy a new idle speed motor?

Sounds like your ISM is OK. It's clean inside and it hums when it should. I'd check for leaks first - see below - but will mention more ISM stuff first.

One more elec verif test for it: Unplug the connector from the top of the ISM. You can see the 3 male connectors on it. Check the DC resistance from the center male spade to each of the outer spades. It should be something like 10-20 Ohms to each outer one but don't quote me.

If you still suspect the ISM see if you can find a D owner nearby who'll lend you a known good one from their car or from their spares pile for a day or two.


Look for air leaking into your intake system. The usual culprits are already mentioned. Decel springs, throttle linkage, loose/cracked hoses or vacuum lines. Also check the injector seals, the distributor advance solenoid and the upper body of the ISM (its seal can crack near the connector). There are threads in this forum about the springs.

To find vac leaks have a mechanic run a smoke test for you if you don't have access to a good smoke machine. It takes less than half an hour.

[glockworks21]

After all the excellent advice from everybody (and greatly appreciated) on what to look for and reading other threads, here is what I did and found. The microswitch does engage when the throttle is at idle. It has continuity. Next, I checked the ECU. Pulled the center side plug and the RPMs increased and decreased when back installed. Then on to the idle speed motor. It was humming/vibrating with the key on BUT the valve did not open when the key was initially turned on. Therefore, I believe I need a new idle speed motor. Am I missing anything before I buy a new idle speed motor?

Andy mentioned the linkage issue. Were you able to check that and maybe re adjust? I too bought a new ism before i adjusted the cables and springs as i was stupidly throwing money at the problem. It did not help. To add insult to injury the new one just failed( a few days ago).. I put the original bosch back in and its perfect. That aftermarket ism was less than a year old..

[r00b]

Andy mentioned the linkage issue. Were you able to check that and maybe re adjust? I too bought a new ism before i adjusted the cables and springs as i was stupidly throwing money at the problem. It did not help. To add insult to injury the new one just failed( a few days ago).. I put the original bosch back in and its perfect. That aftermarket ism was less than a year old..

That sucks, did you get it from one of the vendors?

Ricker, if you do want to try an ISM they are $42 on Amazon https://www.amazon.com/gp/product/B07PMWSL25/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

[Ricker]

The idle speed motor was bad and I did replace it from one from Deloreango.com. That did the trick. Car starts right away at high idle and drops down after just a little. I still think I may have to mess with the air/fuel ration along with the new injectors. We'll see. Thanks for the help!

[r00b]

:wiggle:

[Ricker]

Well, I thought I had the idle issue solved. I don't completely. Sorry, but here is a list of questions to help me understand.

1. I thought the ECU ALWAYS controlled the RPMs at 775. If so, what does the idle throttle plate screw adjustment do? If you set it for high RPMs, the RPMs are greater than the 775. If you set it low, will the ECM maintain the 775 RPMs, or will it run at the lower RPM?
2. When does the ECM control the RPMs and when does the idle throttle plate control the RPMs?
3. The micro switch tells the car the engine should be at idle RPM, right?

Here's the problem. Engine starts fine hot or cold. RPMs are at 900 from the set screw/idle throttle plate. With the lights on, A/C on and in drive it drops to 775 RPMs. However, in neutral and not touching anything, I mean nothing, the idle will now and then go to 1,500 RPMs and after a while back to 900 RPMs. Any ideas?

I just replaced the Idle Speed Motor, Vacuum Hoses are all new. Micro switch is set and is working. Dwell is set. I will admit the engine runs a bit rough/vibrates at idle.

If you still think it might be the deacceleration valves/springs, where are they? If I take off the throttle body, will I see then and clean them with carburetor cleaner provided the issue is just grime?

Could it be the ECU or an issue with one of the inputs?

[WHO1DMC]

Well, I thought I had the idle issue solved. I don't completely. Sorry, but here is a list of questions to help me understand.

1. I thought the ECU ALWAYS controlled the RPMs at 775. If so, what does the idle throttle plate screw adjustment do? If you set it for high RPMs, the RPMs are greater than the 775. If you set it low, will the ECM maintain the 775 RPMs, or will it run at the lower RPM?
2. When does the ECM control the RPMs and when does the idle throttle plate control the RPMs?
3. The micro switch tells the car the engine should be at idle RPM, right?

Here's the problem. Engine starts fine hot or cold. RPMs are at 900 from the set screw/idle throttle plate. With the lights on, A/C on and in drive it drops to 775 RPMs. However, in neutral and not touching anything, I mean nothing, the idle will now and then go to 1,500 RPMs and after a while back to 900 RPMs. Any ideas?

I just replaced the Idle Speed Motor, Vacuum Hoses are all new. Micro switch is set and is working. Dwell is set. I will admit the engine runs a bit rough/vibrates at idle.

If you still think it might be the deacceleration valves/springs, where are they? If I take off the throttle body, will I see then and clean them with carburetor cleaner provided the issue is just grime?

Could it be the ECU or an issue with one of the inputs?Here's a picture of what the deceleration springs look like. There on the butterfly valves of the throttle body.
Throttle body cleaner is what I used.





Dave B.https://uploads.tapatalk-cdn.com/20240226/13b197cb953eb1b8abf2b4c499041f8f.jpg

Sent from my SM-G991U1 using Tapatalk

[Bitsyncmaster]

Well, I thought I had the idle issue solved. I don't completely. Sorry, but here is a list of questions to help me understand.

1. I thought the ECU ALWAYS controlled the RPMs at 775. If so, what does the idle throttle plate screw adjustment do? If you set it for high RPMs, the RPMs are greater than the 775. If you set it low, will the ECM maintain the 775 RPMs, or will it run at the lower RPM?
2. When does the ECM control the RPMs and when does the idle throttle plate control the RPMs?
3. The micro switch tells the car the engine should be at idle RPM, right?

Here's the problem. Engine starts fine hot or cold. RPMs are at 900 from the set screw/idle throttle plate. With the lights on, A/C on and in drive it drops to 775 RPMs. However, in neutral and not touching anything, I mean nothing, the idle will now and then go to 1,500 RPMs and after a while back to 900 RPMs. Any ideas?

I just replaced the Idle Speed Motor, Vacuum Hoses are all new. Micro switch is set and is working. Dwell is set. I will admit the engine runs a bit rough/vibrates at idle.

If you still think it might be the deacceleration valves/springs, where are they? If I take off the throttle body, will I see then and clean them with carburetor cleaner provided the issue is just grime?

Could it be the ECU or an issue with one of the inputs?

Stock idle ECU always tries to hold 775 RPM. Does not matter hot or cold, idle switch on or off.

The idle switch just helps the stock idle ECU control timing when you release throttle quickly. So you don't get RPM undershoot.

The temperature sender controls how much closed the idle motor can do. When cold the idle motor can not close as much as when hot so hence you may get a "cold fast idle". It all depends on your engine oil and curb idle settings.

If you set 900 RPM cold with the curb idle screw, I would expect your 1500 RPM hot is how anyone's engines would run with those settings.

[Michael]

I suspected a ECU was faulty, there is no way to tell for sure without trying a known good one. You can however pull the ECU and look at the board and see if there are any obvious signs such as black spots where something has burned or broken pathways, melted components or damaged capacitors...not seeing these doesn't mean you have a good ecu, but seeing it sure tell you it needs to be replaced.

[82DMC12]

Well, I thought I had the idle issue solved. I don't completely. Sorry, but here is a list of questions to help me understand.

1. I thought the ECU ALWAYS controlled the RPMs at 775. If so, what does the idle throttle plate screw adjustment do? If you set it for high RPMs, the RPMs are greater than the 775. If you set it low, will the ECM maintain the 775 RPMs, or will it run at the lower RPM?
2. When does the ECM control the RPMs and when does the idle throttle plate control the RPMs?
3. The micro switch tells the car the engine should be at idle RPM, right?

Here's the problem. Engine starts fine hot or cold. RPMs are at 900 from the set screw/idle throttle plate. With the lights on, A/C on and in drive it drops to 775 RPMs. However, in neutral and not touching anything, I mean nothing, the idle will now and then go to 1,500 RPMs and after a while back to 900 RPMs. Any ideas?

I just replaced the Idle Speed Motor, Vacuum Hoses are all new. Micro switch is set and is working. Dwell is set. I will admit the engine runs a bit rough/vibrates at idle.

If you still think it might be the deacceleration valves/springs, where are they? If I take off the throttle body, will I see then and clean them with carburetor cleaner provided the issue is just grime?

Could it be the ECU or an issue with one of the inputs?

Answers:
1) ECU will always try to control the RPM's at 775 AT IDLE which means your foot is off the gas and the idle speed microswitch is depressed. It can't do this if the curb idle screw is not set correctly or there is some other vacuum leak, decel springs , etc.

2) ECU controls idle speed only at idle. It does nothing when your foot is on the gas.

3) Yes

If your idle microswitch is flakey, you have a bad wiring connection, or the screw is barely touching the switch, and the switch fails to close AT IDLE, the RPMS will go up to 1,300 or so.

The decel springs are in the throttle body, you can see them if you remove the W pipe from the front of the intake manifold. You can clean them with carb cleaner but they are almost certainly "OK" as long as the look like a coil and evenly spaced / not collapsed.

[Ricker]

Messing around trying to figure out the idle changing issue. I looked at the deacceleration springs and they look OK. I juggled the copper tube (tube of agony) from the ISM to the intake manifold. I think it is not sealed and is an air leak at the intake manifold. The engine RPMs changes. I remember years ago I put a new seal (metal ring with an O-ring in it). Even then I wondered if it really did a good seal. Is there a better way of sealing this? Some kind of RTV sealant with the O-ring thing, put the RTV on it and try to get it back in the hole? What do you need to remove to help make it possible from experience?

I also think the throttle linkage is a bit off, but that is pretty straight forward.

[Bitsyncmaster]

Messing around trying to figure out the idle changing issue. I looked at the deacceleration springs and they look OK. I juggled the copper tube (tube of agony) from the ISM to the intake manifold. I think it is not sealed and is an air leak at the intake manifold. The engine RPMs changes. I remember years ago I put a new seal (metal ring with an O-ring in it). Even then I wondered if it really did a good seal. Is there a better way of sealing this? Some kind of RTV sealant with the O-ring thing, put the RTV on it and try to get it back in the hole? What do you need to remove to help make it possible from experience?

I also think the throttle linkage is a bit off, but that is pretty straight forward.

I used locktite to lock that holding washer in but as long as the correct O-ring is installed it should make a good seal. I also put some grease on the copper pipe which may also help with sealing.

[Ricker]

Well now I did it. After messing with a bunch of things, here is what it does now. When in drive, lights on, A/C on or both off, it idles nicely at the 775 RPMs. However, now when in Park it idles at 1,850 RPMs but consistently (that's an improvement). And this is with the throttle linkage disconnected and the throttle plates closed and the microswitch engaged. Will start all over tomorrow checking everything again. Stupid car!

[Ricker]

Well now I did it. After messing with a bunch of things, here is what it does now. When in drive, lights on, A/C on or both off, it idles nicely at the 775 RPMs. However, now when in Park it idles at 1,850 RPMs but consistently (that's an improvement). And this is with the throttle linkage disconnected and the throttle plates closed and the microswitch engaged. Will start all over tomorrow checking everything again. Stupid car!

Now I'm thinking that there is not an air leak. But with the throttle completely closed and high RPMs, there has to be fuel coming from the Cold Start Valve (CSV). I will check this tomorrow by pulling the electrical connection. If it is adding fuel even when the engine is hot, then it is the temperature sensor. But why would the ISM be open to allow fuel to the engine? How do the CSV and ISM tie together?

[Michael]

I doubt the CSV is leaking.

Have you pulled and checked the idle computer?

Also wouldn't be a bad idea to double check the curb throttle setting. This gets the idle close without the computer working so much.

And when you checked the microswitch, did you use the ohms setting? Sometimes the switch goes bad but may test good but it's turned into a giant resistor.

If you want to bypass the switch, I would imagine you could just short the terminals together and eliminate the switch for testing purposes. Someone tell me if that's a bad idea.

[82DMC12]

Also agree it is not the CSV leaking.

You need to first follow Dave's advice and make sure the pipe of pain is installed correctly and the o-ring is in place. Grease it with Red Rubber Grease. You can see the tip of the pipe poking into the air meter housing if you push down on the meter plate and look in with a flash light. Make sure you can see all of the beveled edge inside the air meter.

The throttle can act screwy when you don't have the linkage installed. The springs in the throttle spool are supposed to help close the throttle butterflies. I think you need to start at the throttle butterfly and reset all of your linkage. Here are some tips, and do this in order since the order is important:



Confirm the throttle cable is in excellent shape and not shredding where it comes out of the black sheath in front of the spool. Replace the inner cable if at all questionable, this is a safety item. You can easily replace it by pushing a new cable up from the gas pedal footwell.
Disconnect the throttle cable from the spool and disconnect the linkage arm from the bottom of the spool
Back off both idle stop screws (curb idle and microswitch screw) so they are not influencing anything else
with the linkage disconnected, clean and then grease the springs both on the butterfly rod and the throttle spool with white lithium grease so you are sure they are not binding.
Make sure the throttle arm (the thing with the two idle set screws in it) is centered on the threaded rod for the butterflies and the nut that holds it on is tight. Make sure the arm is not twisting on the rod because it's loose. That will give unpredictable results.
connect the throttle linkage to the spool. Shorten it sufficiently so that the idle stop finger on the spool is about 1/4" away from the stop post. It is NOT supposed to be touching the post.
Now with the W pipe off, turn the spool to full throttle (so the full throttle finger is actually touching the stop) and make sure the butterflies are opening completely at full throttle. You won't be able to make them open exactly perpendicular, but they will be just short of fully opening. Move the full throttle switch away from the FTS finger if it's interfering with the throttle spool itself hitting the stop.
Now wrap around and connect the throttle cable to the spool smartly so that is somewhat taut but not affecting the throttle spool position. Do not try to take up all the slack. The cable shouldn't be loose but it can't be tight either.
Disconnect the linkage arm from the bottom of the spool and shorten it about 2mm. You should have to open the throttle SLIGHTLY by turning the throttle spool in order to get the linkage arm is connect to the ball underneath. There has to be some pre-tension here.
Now the throttle is basically set up. Screw in the microswitch screw so it definitely engages the idle speed switch and give it another half turn and lock it down.
Start the car and it should be idling at 775. Wait until the engine is HOT and then slowly turn the curb idle screw IN , a tiny bit at a time, until it contacts the curb idle stop plate. Now each time you turn the curb screw in, do the same amount for the idle speed switch screw so that the pressure is even on both screws.
Keep doing this SLOWLY until you can hear the engine idle speed increase due to the curb idle screw being too far in. Back it off so it is just on the edge of opening the throttle (increasing idle speed). Lock the curb idle screw down.
Unscrew the idle switch screw until it opens the idle switch and RPM's go up to 1,300 - 1,700 (switch is off). Now turn it back in until the switch is engaged, and give it an additional 3/4 turn. Now lock it in.
Now using the ferrule that the throttle cable runs through before going to the spool, loosen the lock nut and adjust the ferrule until the throttle cable is, once again, somewhat taut but not slack and not able to pull on the spool at rest. Now lock the nut down.


Throttle should be adjusted properly now. If you come to a stop sign and sometimes the idle is SLIGHTLY too high, you need either SLIGHTLY loosen the ferrule or SLIGHTLY back off the curb idle screw. That will correct intermittent BARELY elevated idle at stop signs etc.

[Ricker]

Spent today checking everything again. First, did the throttle adjustment like suggested above (lots of detail!). Long story short the microswitch is bad. When the engine is idling ONLY, I jumper it out and the RPMs came down. Second, I noticed when the engine is cold, RPMs are correct but go to 775 right away, like in 3 seconds. When the engine gets hot the RPMs increase without doing anything. So, I stop the engine while hot, pulled the plug on the thermotime switch and checked the ohms. With the ground to the engine block, one pin read 59 ohms the other 117 ohms (I thought this is supposed to be 0). Ok, so did I do something wrong or is the switch bad? Just to check thermotime switch is the one on the front of the engine (back of the car) and down by the water pump? Also, this switch would change the RPMs dependent on the engine temperature, right?

Are these only available from a Delorean parts guy?

[Michael]

Not sure about thermotime readings but it doesn't matter. That doesn't affect idle anyway. In fact, many people simply unplug it in the summer temps.

I think you found a major piece with the microswitch. Once curb idle is set and the switch is replaced you can start more on zeroing in on the culprits.

The two things that come to mind are (as I said before), bad ecu and/or intake leak. I don't really know the history of the car so I'm just throwing out common possibilities. Also don't forget the early advice of sticking or dirty throttle components/cable.

[Ricker]

I started the car in Park. Pulled the plug on the Thermo Time Switch. Jumpered the Microswitch. The Curb Idler Screw is not touching. The Butterflys are completely closed (I removed the U-Pipe and checked).
Once the car got hot the RPMs went up from 775 to 1,500. It starts find when hot. I pulled the center side plug on the ECU and the RPMs went up to 2,200. Plugged it back in and down to the 1,500 (cause the engine was hot). Plugged the Thermo Time Switch back in, made no changes.

Something is telling the car when hot to increase the idle RPMs. What? The ECU, some sensor? Why only when hot?

[Bitsyncmaster]

I started the car in Park. Pulled the plug on the Thermo Time Switch. Jumpered the Microswitch. The Curb Idler Screw is not touching. The Butterflys are completely closed (I removed the U-Pipe and checked).
Once the car got hot the RPMs went up from 775 to 1,500. It starts find when hot. I pulled the center side plug on the ECU and the RPMs went up to 2,200. Plugged it back in and down to the 1,500 (cause the engine was hot). Plugged the Thermo Time Switch back in, made no changes.

Something is telling the car when hot to increase the idle RPMs. What? The ECU, some sensor? Why only when hot?

With all those symptoms, my guess is you have leaking deceleration springs. Did you look at springs?

Here is a photo of bad springs.

[Ricker]

With all those symptoms, my guess is you have leaking deceleration springs. Did you look at springs?

Here is a photo of bad springs.

I have. Here is a photo of mine. Do they look bad?

https://dmctalk.org/images/attach/jpg.gif (not sure how to add a picture)

[Bitsyncmaster]

I have. Here is a photo of mine. Do they look bad?

https://dmctalk.org/images/attach/jpg.gif (not sure how to add a picture)

Hard to see in that photo but I think I see uneven spacing which has shown the springs are a problem.

[Michael]

Edit...found this on the euro forum. It may help

This info is courtesy of Nick T, who imparted his secrets to me in a call last year. I have only just got round to making use of the info, and I must say it has made a real difference to the feel of the car.

It became necessary on my own car when I noticed a high idle, and traced it to the butterflies not closing fully at “rest”. Coincidentally this high idle became noticeable after fitting the new exhaust and Nick helped Dan K set up the mixture. After getting it "ballpark", and adjusting fuel pressures accordingly, I noticed a high idle once the car was fully warm.

(The rest of the D-Intelligence gleaned in the phone call will be written up after I have done it myself).

Following this procedure will allow correct set up of the mechanics of the throttle control from pedal to butterflies. Nothing too radical, just useful information- mine was a definite bodge.

To start from first principles is often the best way. I also replaced the throttle cable, making sure it was well lubed.
1. Disconnect the linkage rod front the ball joint on the throttle spool.
2. Unwind the top grub screw, on the “butterfly actuating lever” away from the idle microswitch
3. Back off the bottom (throttle stop) screw on the same lever, so that its off the stop.
4. Screw this back in, until it just touches the stop. Then give it one more full turn and nip up the locknut
5. Grab the link rod, and open and close the mechanism. It should be smooth and repeatable. You may wish to visually check the butterflies are closing fully. I had taken mine off previously, so knew they were good. If this is all ok, clean and lubricate the return spring.
6. Get a 0.3mm (12 thou) feeler gauge between the closed throttle stop screw and the the throttle stop.
7. Open the throttle very slightly, and adjust the top idle microswitch activating screw, so that it just activates the microswitch (“click”) at this point. Nip up the locknut.
8. Now look at the spool.
9. At zero throttle, it should rest on the zero stop.
10. Similarly at full throttle (pedal fully depressed) the spool must touch the 100% stop
11. If not, adjust the pedal stop in the drivers footwell to ensure the spool fully closes at rest and the spool goes to 100% when the pedal is fully depressed. Ideally, the cable adjustment (where the cable goes through the throttle spool mounting) will be about halfway along the threaded portion.
12. At 100% throttle, the actuator must also trigger the full throttle microscwitch.
13. Now reattach the connector rod back onto the spool. Adjust the linkage (shorter usually) until the spool is just off the closed stop at rest.
14. Next turn attention to the 3 brass screws…. But that, children, is another story!

More to come when I get further into my set up! At the same time I had replaced my fuel lines, and vac pipes so was reasonably confident of no major vac leaks.

[82DMC12]

Thermotime switch should read about 0 ohms (direct to ground) on one pin to ground and the other pin should read 20 to 30 ohms to ground.

[82DMC12]

Notice that the butterfly plates are not supposed to be 100% closed at idle, they will bind if you try to get them perpendicular. See the process I posted earlier - as you turn in the idle stop screw, you are opening the plates. When you let off the gas, the throttle should spring closed and stop on the stop screw.

Agreed that the spring on the left side of the throttle looks collapsed. You could try to use a hot glue gun and glue the decelleration spring plates closed temporarily as you try to sort this out. If your idle is fixed with the plates glued closed, you will know for sure it's the collapsed spring.

I had an issue with idle creeping up when the engine was hot (after starting cold and just idling in the garage). The problem was just the throttle linkage was not adjusted properly.

[Ricker]

I have done everything suggested and the car still idles at 1,500 RPMs when hot (not cold - 775 RPM) and in park/neutral. So a few more questions......

1) Does the ECU control the idle RPMs when a) in drive and b) in park/neutral? I believe it does.

2) What tells the ECU the temperature of the engine? I know it is not the TTS but something does.

[Bitsyncmaster]

I have done everything suggested and the car still idles at 1,500 RPMs when hot (not cold - 775 RPM) and in park/neutral. So a few more questions......

1) Does the ECU control the idle RPMs when a) in drive and b) in park/neutral? I believe it does.

2) What tells the ECU the temperature of the engine? I know it is not the TTS but something does.

The idle ECU does try to hold 775 RPM all the time. It does not know if in park or neutral.

There is a thermistor (changes resistance with temperature) in the Y pipe that provides the measurement of engine temp to the idle ECU. note: the schematic calls that the "IDLE SPEED REG SW".

[FABombjoy]

I didn't see anything in this thread about ignition timing. Have you checked it?

It's easy to get high RPM with too much idle advance. Like if the solenoid is bad, disconnected, maybe vac hoses backwards at the solenoid.

[Ricker]

The idle ECU does try to hold 775 RPM all the time. It does not know if in park or neutral.

There is a thermistor (changes resistance with temperature) in the Y pipe that provides the measurement of engine temp to the idle ECU. note: the schematic calls that the "IDLE SPEED REG SW".

I checked the thermistor when the engine is cold. I do not get any reading with the ohm meter. I believe it needs replaced and possibly this has been my problem. Your thoughts?

[82DMC12]

I checked the thermistor when the engine is cold. I do not get any reading with the ohm meter. I believe it needs replaced and possibly this has been my problem. Your thoughts?You should have 8000 - 12000 ohms on the thermistor when cold. If it's open circuit then yep it's either bad or the plug is disconnected, if you are trying to measure it at the ECU. Where are you measuring at? You have the intake off?

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[Ricker]

You should have 8000 - 12000 ohms on the thermistor when cold. If it's open circuit then yep it's either bad or the plug is disconnected, if you are trying to measure it at the ECU. Where are you measuring at? You have the intake off?

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I'm under the car and pulled the plugs. Tried the reading directly at the thermistor.

[82DMC12]

Sounds like you're on to something!

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[Ricker]

First, I changed out the Thermo Time Switch. Now the RPMs when the engine is warm it goes up to only 995 RPMs. I then had to adjust the dwell again.

Second, dummy me, thought the Idle Speed Thermistor was under the car on the driver's side. This is the cooling fan thermostat. So where is the Idle Speed Thermistor located. It is near the Y-Tube. Where is that? Any pictures or directions I can follow, I am having a mental block or something. Grrrrr. The way the car is idling now, not sure it needs to be replaced but would like to check it.

[82DMC12]

It is in the y-pipe and has a black two-pin Bosch plug going into it

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[Bitsyncmaster]

First, I changed out the Thermo Time Switch. Now the RPMs when the engine is warm it goes up to only 995 RPMs. I then had to adjust the dwell again.

Second, dummy me, thought the Idle Speed Thermistor was under the car on the driver's side. This is the cooling fan thermostat. So where is the Idle Speed Thermistor located. It is near the Y-Tube. Where is that? Any pictures or directions I can follow, I am having a mental block or something. Grrrr. The way the car is idling now, not sure it needs to be replaced but would like to check it.

Thermal Time Switch only affect engine starting. It provides the ground for the cold start valve. It would not affect idle RPM or dwell. If those changed, something else made those changes.

The idle speed thermistor is in the Y-pipe which is under the intake manifold. You really need to pull the manifold to get access to it. I would check if it works at the bulkhead connectors before going to the effort to get to the thermistor.