Another high idle thread - how-to on butterfly plate springs?

[jawn101]

Hey all. So, this issue has been plaguing me for years and I've finally decided it's time to tackle it.

Same old story. Car turns over perfectly every time, initially the idle is a smooth 750.

After some warm-up or driving, the idle will raise to 900-1000. Blipping the throttle doesn't help it. Shutting the engine off entirely and restarting it, however, does. If I get out and push the throttle arm closed in this state, it doesn't change anything.

This leads me to believe that it's not mechanical, to do with the quadrant arm, throttle spool, etc at this point, but rather perhaps vacuum related. All of my vacuum hoses are new and silicone (and have been recently done, without helping this issue).

I remember ages ago Elvis was quite hot on the notion of cleaning and maintaining the decel valves on the butterfly plates. I know that these might stick slightly and cause a higher idle.

My theory right now is that it makes sense that shutting the engine off entirely and restarting it would remove any air backpressure. This in turn is allowing them to close fully and resetting my timer on the high idle for a bit.

But now I can't find that thread he created about maintaining those springs. Getting the throttle body out is a fairly quick job, but I can't remember if he was advocating for new springs (and if so where to get them) or a good way to check/revitalize the existing ones.

Anyone have a link, a guide, or any other advice? My theory may also make no sense and I'm open to that. But this engine has been overhauled several times and all the new plugs, wires, injectors, fuel lines, water/vacuum hoses and gaskets in the world have not changed this one lingering issue.

[Ron]

First, double check that the vacuum routing going to the vacuum solenoid is correct. If the two are backwards, it will act normal until you rev the engine, then hold the advance a little high until you shut the engine off because it can't vent correctly.

[jawn101]

First, double check that the vacuum routing going to the vacuum solenoid is correct. If the two are backwards, it will act normal until you rev the engine, then hold the advance a little high until you shut the engine off because it can't vent correctly.

Oooh, interesting. I hate that solenoid on the diagram because it's like...basically impossible to tell :lol:

Will do that now. It should only take an hour :smile:

[jawn101]

OK, that was easier than I remembered it being. The confusing part of the diagram I was remembering is actually the CSV tube.

Solenoid is hooked up correctly.

[Bitsyncmaster]

Everything but the shutting the engine off fixes it sounds like bad deceleration springs. So how long does that shutting off fix it? The springs should only open after you release the throttle quickly.

[jawn101]

Everything but the shutting the engine off fixes it sounds like bad deceleration springs. So how long does that shutting off fix it? The springs should only open after you release the throttle quickly.

Uh, not very long. A minute or two maybe?

[Jonathan]

Jon, I've surprised myself more than once on how much things improve by cleaning ground connections. If your issue isn't mechanical because pushing the idle microswitch with your finger doesn't change anything, I'm thinking that could leave electrical as the culprit. i.e. the engine is doing this inadvertently because the signals aren't great. The idle control system wires go off in a lot of different directions and get influenced by more than one ground connection. Some that come to mind that could be affecting this on your car are the big jumble of them on top of the intake on the driver's side toward the front of the car. Right beside where the idle speed motor mounts to the intake. That is also where a slim ground wire connects from the ballast resistor bracket. In addition, the O2 sensor ground is the connection on the passenger side of the intake, sometimes hidden by the plastic air filter box. It has a quick connect on the end of a short red wire that screws into the intake (on the side of the aluminum and not the top IIRC). This is where I would start, given what you've described and done so far.

[jawn101]

Jon, I've surprised myself more than once on how much things improve by cleaning ground connections. If your issue isn't mechanical because pushing the idle microswitch with your finger doesn't change anything, I'm thinking that could leave electrical as the culprit. i.e. the engine is doing this inadvertently because the signals aren't great. The idle control system wires go off in a lot of different directions and get influenced by more than one ground connection. Some that come to mind that could be affecting this on your car are the big jumble of them on top of the intake on the driver's side toward the front of the car. Right beside where the idle speed motor mounts to the intake. That is also where a slim ground wire connects from the ballast resistor bracket. In addition, the O2 sensor ground is the connection on the passenger side of the intake, sometimes hidden by the plastic air filter box. It has a quick connect on the end of a short red wire that screws into the intake (on the side of the aluminum and not the top IIRC). This is where I would start, given what you've described and done so far.

Good thinking, but the idle microswitch is already engaged when the throttle is closed; and if I open the throttle by hand in the engine bay and disengage the switch I can tell that it's definitely having an impact on the running condition. I did the grounds a few years ago in the car and everything else is rock solid, including a direct 2ga cable from the battery directly to the transmission and Dave's relay strip buses.

I'll still double check the small grounds you mentioned at the top of the intake - they're easily accessible and could easily have been jostled or damaged with all the top end work I've done recently. But from my own observations that doesn't feel right.

[jawn101]

Jonathan: quick update, I went and checked those top top end grounds. Everything good to go, I did polish the ring terminal for the 456 bank one but it was really fine, just cosmetic there.

After another couple start tests (including an unrelated issue with a popped out injector, my fault) it seems that I might be mistaken about shutting off/restarting causing the idle to go back down. I did a few starts in fairly rapid succession and it was sticking in the high 900s each time after the initial warm up at ~775.

[Bitsyncmaster]

Post a photo of the deceleration springs. You pull the W pipe and move the throttle and you can see them. If they are not evenly spaced, they are bad.

[jawn101]

Post a photo of the deceleration springs. You pull the W pipe and move the throttle and you can see them. If they are not evenly spaced, they are bad.

Okie doke. Here are the pics. TBH, these look pretty ok to me.


61784

61783

61782

[Bitsyncmaster]

Okie doke. Here are the pics. TBH, these look pretty ok to me.


61784

61783

61782

Yes, those look good.

[jawn101]

Hmm. Then what else could it be? I had a friend suggest that the idle motor might be sticking, I haven’t investigated that yet.

[David T]

One possibility is that the throttle arm is not being returned ALL the way to the idle stop position. That can happen if you develop a lot of play (looseness) in the rod ends of the quadrant link or the throttle cable or throttle spool is sticking and not moving smoothly and easily. Verify that the idle switch is getting "set" when you release the gas pedal. If anyone messed with the idle stop screw and/or the idle switch adjustment the throttle plates may not be fully closed and if the air screws are not closed air can be bypassing through them. Just a few more things to check.

[jawn101]

One possibility is that the throttle arm is not being returned ALL the way to the idle stop position. That can happen if you develop a lot of play (looseness) in the rod ends of the quadrant link or the throttle cable or throttle spool is sticking and not moving smoothly and easily. Verify that the idle switch is getting "set" when you release the gas pedal. If anyone messed with the idle stop screw and/or the idle switch adjustment the throttle plates may not be fully closed and if the air screws are not closed air can be bypassing through them. Just a few more things to check.

Thanks, but as I mentioned the quadrant arm and throttle spool seem mechanically correct, and the idle switch is engaged. Both screws have their factory paint marks intact and nobody's touched them. Brass screws are all closed tight. Pushing the throttle arm "more closed" when the idle raises while warm doesn't change anything.

[David T]

Well, you are getting "false air" leaking in somewhere then. Either you find it visually or you do a smoke test to find the leak. A missing gasket, a leaky hose, something. On one car I found a leak, it was on the right side intake runner, front surface, the seal plug was squished because someone used too long a bolt on the ground connection and it bent the seal plug. Vacuum leaks can be difficult to find. On another car the "O" ring was missing on the cold start valve. Often the injector seals leak. Also common for the tube to the idle motor "O" ring on the bottom of the mixture unit. Point is you have to look for the unusual.

[jawn101]

Yeah, a smoke test isn't a bad idea. I just replaced the injector seals a few weeks ago, actually - new clips, too. I know the CSV has the O-ring on it, and the idle air pipe has a new o-ring as well as RTV holding the brass cup down just to be sure.

I do know that the oil filler cap doesn't seal, and I've tried replacing the o-ring but it never seems to be the right OD. It sort of floats on top of the neck. Also my dipstick doesn't seat fully; it doesn't seem that the rubber portion can be moved on the metal, and I don't want to nip the end of the stick since that would impact how it measures (not that I use it for that)

The odd thing remains that this is only happening warm. Wouldn't a vacuum leak be present no matter what?

[jawn101]

Just a little more troubleshooting: I removed the idle motor and sprayed it out with some penetrating oil, through the intake side only. It really wasn't very gross inside. Reattached it and made sure the seals to the idle air/CSV pipes were good. Didn't really make a difference.

Now, on day 3 of fiddling with things, it does seem like pressing the throttle arm hard closed against the body changes the RPM. The microswitch is engaged, but mechanically it seems that something is still ever so slightly open internally. I tried adjusting the length of the quadrant arm slightly, you can do it in half turns if you flip it end over end - but that seemed to make it worse.

[Bitsyncmaster]

Two things on my car:

The throttle cable had worn through the outer rubber where it was clamped on the passenger side valve cover.

Greasing the large throttle spring on the spool fixed my sticking throttle return.

[jawn101]

Two things on my car:

The throttle cable had worn through the outer rubber where it was clamped on the passenger side valve cover.

Greasing the large throttle spring on the spool fixed my sticking throttle return.

Ugh, that long ass cable is the bane of my existence. Nobody ever intended that style of cable to be used like this. I did have an issue with the throttle sticking open that turned out to be me pinching the cable between the valve cover and airbox, which I resolved.

There are two main springs back there, the one on the armature itself (vertically oriented, attached to throttle body) and the one inside the spool. I *normally* run without the one in the spool at all, since it makes throttle response way snappier, but I've reinstalled it to eliminate that as a source of problem here. I'm sure they could both do with some grease, but which did you mean? Sounds like the removable one?

[Ron]

No, heat expansion can make some vacuum leaks come and go.

======

Uggg, the symptoms are changing a lot...

Maybe take the throttle linkage loose, let it warm up and try it.
If it does't stay high after several tries, it's probably the linkage.

[jawn101]

No, heat expansion can make some vacuum leaks come and go.

======

Uggg, the symptoms are changing a lot...

Maybe take the throttle linkage loose, let it warm up and try it.
If it does't stay high after several tries, it's probably the linkage.

So, disconnect the quadrant arm and leave it running at idle for a while, without any throttle movement?

[Ron]

Yes. And give it a good chance to raise on its own. If it don't, raise it with the arm and see if that does it. (Anything to get something consistent going on).

[David T]

If you notice that you think you have vacuum leaks dependent on whether the car is hot or cold you need to investigate all of the vacuum systems. Some of them operate differently hot and cold. First do a visual inspection for routing and disconnected hoses. See if they are hard and brittle. Look for cracks. Make sure everything is hooked up and working. Look up Service Bulletins ST-18-10/81 and ST-32-12/81. It really matters how the vacuum advance solenoid is hooked up so check it carefully. Make sure it clicks. The quadrant link is a lefty-righty threaded rod. It can be very precisely adjusted in place but only if it is not worn. If it is worn, adjust it so it pushes the throttle arm to idle. You will have a bit of extra play when you step on the gas pedal but it will always go to idle. If you try to take the quadrant link out remember it has those tiny little clips like the struts do that MUST be removed first! To adjust it you just loosen the jam nuts and turn the rod.

[jawn101]

If you notice that you think you have vacuum leaks dependent on whether the car is hot or cold you need to investigate all of the vacuum systems. Some of them operate differently hot and cold. First do a visual inspection for routing and disconnected hoses. See if they are hard and brittle. Look for cracks. Make sure everything is hooked up and working. Look up Service Bulletins ST-18-10/81 and ST-32-12/81. It really matters how the vacuum advance solenoid is hooked up so check it carefully. Make sure it clicks. The quadrant link is a lefty-righty threaded rod. It can be very precisely adjusted in place but only if it is not worn. If it is worn, adjust it so it pushes the throttle arm to idle. You will have a bit of extra play when you step on the gas pedal but it will always go to idle. If you try to take the quadrant link out remember it has those tiny little clips like the struts do that MUST be removed first! To adjust it you just loosen the jam nuts and turn the rod.

All good tips. Will verify the vacuum routing is right from the thermal switch in the valley, everything on the top end is visibly correct. All the hoses are new silicone, nothing brittle or cracked.

Curious, how can I verify the vacuum solenoid is clicking? It is visibly connected right, electrical and vacuum. The electrical connection tests good, but if there's a way to feel/tell if it's actually engaging and not burned out internally that would be valuable. What's the test for that look like?

[Ron]

Pull the hose off of the distributor and feel it for vacuum.
First, there should be no vacuum on the hose when the engine is cold. If there is, the valve or connection(s) in the VOD has a problem.

Once the engine is warm:
There should be no vacuum on the hose at idle.
There should be vacuum on the hose when you raise the RPM.

You can do also this with a timing light, but you have to allow for the distributor adding advance mechanically (hot or cold).

[jawn101]

Pull the hose off of the distributor and feel it for vacuum.
First, there should be no vacuum on the hose when the engine is cold. If there is, the valve or connection(s) in the VOD has a problem.

Once the engine is warm:
There should be no vacuum on the hose at idle.
There should be vacuum on the hose when you raise the RPM.

You can do also this with a timing light, but you have to allow for the distributor adding advance mechanically (hot or cold).

I think I may have made a mistake in my test protocol here, so the engine is cooling down and I will try again in a few hours. Here's what I did/observed:

1. Disconnected quadrant arm from throttle spool, left it hanging
2. Started engine, cold having sat overnight - idle at about 775
3. Removed vacuum hose from solenoid to distributor, at the distributor end and felt it for vacuum. None there.
4. Let the motor warm up for about 10 minutes
5. Observed that the idle did in fact raise slightly, to about 1000 even with the quadrant arm disconnected
6. Pressed on the upper idle screw (the one that actuates the idle microswitch) - idle dropped some
7. Pulled the vacuum hose from the distributor again, still no vacuum there
8. Decided to check the hose inbound to the solenoid from the thermal switch in the valley - plenty of vacuum (at idle, engine now warm)

What I didn't test was:
1. Did vacuum manifest on the output air line from the solenoid, with the RPMs raised
2. Was there vacuum on the hose leading from the valley to the solenoid when the motor was cold (testing switch/routing)

At this point I'm anticipating that when I re-do the test, I will find that the vacuum behavior between the switch in the valley and the solenoid/distributor is as expected, and the issue is actually to do with adjustment of those set screws for the microswitch/pivot point. I've never, ever touched those and I believe I recall that conventional wisdom was that you shouldn't. But I feel like if I back the lower one off a bit to move the fulcrum just a hair, then pick up the slack in the quadrant arm, it might resolve all of this.

[jawn101]

Ok, so... there is vacuum to the center post of the vacuum solenoid, even at cold idle. That’s the hose that comes directly from the thermal switch.

Does this mean something is hooked up backwards in the valley? I can swap the hoses that go to the solenoid and WUR, there’s enough slack to give that a try without opening the intake. Should I do that?

I also confirmed that there is no vacuum coming from the solenoid to the distributor at idle, but when I open the throttle the vacuum there is strong.

[Ron]

Ok, so... there is vacuum to the center post of the vacuum solenoid, even at cold idle. That’s the hose that comes directly from the thermal switch.

Does this mean something is hooked up backwards in the valley?
It means that the the thermal vacuum switch is failing to switch vacuum to the WUR/CPR when it is cold.


..., but when I open the throttle the vacuum there is strong.
This and symptoms 1, 7, 8 means the solenoid and switch should operate correctly when the valve is fixed. Confirm it is bad by checking to see if the WUR/CPR has vacuum when it is dead cold.
If it don't have vacuum cold the valve is not doing its job. If it does, the valve might be sending vacuum to both all the time...

Sounds like you need to adjust the linkage to make it favor shut (as mentioned above) and maybe test the microswitch using a tiny screwdriver w/o disturbing anything else while it is revved up on its own.
And connect a spare hose to the distributor and draw on it to making sure it is holding vacuum and not the source of a leak.

[jawn101]

It means that the the thermal vacuum switch is failing to switch vacuum to the WUR/CPR when it is cold.


This and symptoms 1, 7, 8 means the solenoid and switch should operate correctly when the valve is fixed. Confirm it is bad by checking to see if the WUR/CPR has vacuum when it is dead cold.
If it don't have vacuum cold the valve is not doing its job. If it does, the valve might be sending vacuum to both all the time...

Sounds like you need to adjust the linkage to make it favor shut (as mentioned above) and maybe test the microswitch using a tiny screwdriver w/o disturbing anything else while it is revved up on its own.
And connect a spare hose to the distributor and draw on it to making sure it is holding vacuum and not the source of a leak.

Roger that, I will test the vacuum again when the car has sat for a few more hours to cool. If there is *not* vacuum at the WUR when cold, is it possible the hoses were simply placed on the thermal switch backwards? I did a valley job to put new water hoses in a few weeks ago and a lot of these idle issues have cropped up or become more obvious since then. If that's the case, my test of just swapping the hose to the center nipple on the solenoid and the hose feeding the plastic T on the WUR should be helpful - and a possible temporary fix?

Will work on the throttle adjustments only after I rule out these other factors.

Thanks as always Ron!

[Ron]

Roger that, I will test the vacuum again when the car has sat for a few more hours to cool. If there is *not* vacuum at the WUR when cold, is it possible the hoses were simply placed on the thermal switch backwards?
In #8, you had vacuum going to the solenoid when warm, as it should be. If they were backwards, you would not have had vacuum then...

Cold you want:
Vacuum from thermal vacuum control valve to WUR/CPR
No vacuum to solenoid (so, no vacuum to distributor, switch doesn't matter).

Warm you want:
No vacuum from thermal vacuum control valve to WUR/CPR.
Vacuum to solenoid.
No vacuum to the distributor at idle (switch is pressed).
Vacuum to distributor above idle (switch is not pressed).


I did a valley job to put new water hoses in a few weeks ago and a lot of these idle issues have cropped up or become more obvious since then. If that's the case, my test of just swapping the hose to the center nipple on the solenoid and the hose feeding the plastic T on the WUR should be helpful - and a possible temporary fix?

Will work on the throttle adjustments only after I rule out these other factors.

Thanks as always Ron!
If you have vacuum to the WUR/CPR when cold, then the thermal vacuum control valve is incorrectly sending vacuum to both...If nothing has changed.
If I'm following you- If they were backwards, swapping the end at the WUR with the end at the center nipple on the solenoid would be a permanent fix.

YW!

[jawn101]

In #8, you had vacuum going to the solenoid when warm, as it should be. If they were backwards, you would not have had vacuum then...

Cold you want:
Vacuum from thermal vacuum control valve to WUR/CPR
No vacuum to solenoid (so, no vacuum to distributor, switch doesn't matter).

Warm you want:
No vacuum from thermal vacuum control valve to WUR/CPR.
Vacuum to solenoid.
No vacuum to the distributor at idle (switch is pressed).
Vacuum to distributor above idle (switch is not pressed).


If you have vacuum to the WUR/CPR when cold, then the thermal vacuum control valve is incorrectly sending vacuum to both...If nothing has changed.
If I'm following you- If they were backwards, swapping the end at the WUR with the end at the center nipple on the solenoid would be a permanent fix.

YW!

Alrighty. Just did this all again. No vacuum at the center nipple on the solenoid cold, vacuum at the WUR instead. Unplugging the vacuum supply to the WUR during warmup significantly worsened the running condition, so it’s doing it’s job. After warmup, the vacuum supply was reversed as expected. So, that ain’t it.

I guess it’s just down to adjusting those mechanical parts a bit. And I’d sure love to find a way to make the oil filler cap seal better, the hoses to it are constantly oil-filmy.

All of this hyperattention to vacuum and idle quality has me wondering if the whole motor doesn’t sound a little....chuggy. Something for another day, it might also just be the smooooooooth sounds of an odd fire V6. Need to compare it to a buddy’s.

[Ron]

Alrighty. Just did this all again. No vacuum at the center nipple on the solenoid cold, vacuum at the WUR instead. Are you thinking you didn't let it cool off enough during the test before (post 8 )? Or, another change?

Assuming you checked the distributor for a vacuum leak?


I guess it’s just down to adjusting those mechanical parts a bit. And I’d sure love to find a way to make the oil filler cap seal better, the hoses to it are constantly oil-filmy.
I don't see it causing all of the symptoms, but a bad o-ring on the cap is a vacuum leak...Take it to a large auto parts and get them to match out a replacement if worn. Otherwise, get a slightly larger one and/or used more than one. (Take the D with you and check the fit before you leave...;-)

If the distributor isn't leaking vacuum, I agree it's time to try making it close tighter.

[FABombjoy]

Unplugging the vacuum supply to the WUR during warmup significantly worsened the running condition, so it’s doing it’s job.
The vacuum at the WUR is part of a cold acceleration enrichment circuit. If you removed the vacuum line, plugged it, and it still ran worse after a few seconds that's unusual.


And I’d sure love to find a way to make the oil filler cap seal better, the hoses to it are constantly oil-filmy.
Get rid of the silicone hoses there. Plain silicone hose is not suitable for crankcase ventilation. Pick up emissions-rated vacuum hose from any auto parts store and it'll stop.


I don't see it causing all of the symptoms, but a bad o-ring on the cap is a vacuum leak..
Not significantly from a fueling standpoint as its through the fixed orifice. The free oxygen in the crankcase vapors would be slightly less but it also mingles with the fresh air from the air filter hose. Not to say he shouldn't fix a loose O ring problem but the oily hoses are from the use of silicone.

[Jonathan]

And I’d sure love to find a way to make the oil filler cap seal better, the hoses to it are constantly oil-filmy.


Get rid of the silicone hoses there. Plain silicone hose is not suitable for crankcase ventilation. Pick up emissions-rated vacuum hose from any auto parts store and it'll stop.

A question about this as I have the same oil-filmy-ness on some of my hoses.

Is this a matter of the oil actually permeating its way through the hose? Like in a tiny, pore size way?

I put in a replacement silicone, nice blue coloured hose kit and this is exactly what I see on more than one of those hoses going either in or out of the charcoal canister area or to and from the oil filler.

Sounds like proper rubber hoses are what is best here? Although I only see the silicone hose sets for sale. On the DeLoreanGO page anyway. Houston has them individually, original rubber ones I would assume, but no kits that I could see.

[FABombjoy]

Oil rated or fuel rated hose will cure the problem. Parts stores will sell PCV rated hose, but you could use oil cooler, trans cooler, or fuel hose too. It just gets more expensive and less flexible if you use fuel/oil hose vs emissions hose.

https://www.instructables.com/id/Why-Silicone-Hoses-Cannot-Be-Used-for-Oil-and-Fuel/

[jawn101]

Are you thinking you didn't let it cool off enough during the test before (post 8 )? Or, another change?

Assuming you checked the distributor for a vacuum leak?


I don't see it causing all of the symptoms, but a bad o-ring on the cap is a vacuum leak...Take it to a large auto parts and get them to match out a replacement if worn. Otherwise, get a slightly larger one and/or used more than one. (Take the D with you and check the fit before you leave...;-)

If the distributor isn't leaking vacuum, I agree it's time to try making it close tighter.

Hey Ron - so I didn’t test the vacuum *inbound* to the solenoid from the valley when the car was cold on the first test. That was my screwup as it left me with no control value for the cold symptoms.

So it seems to me that these connections are good. I’m not sure how to test the distributor as a leak source, do you have a test in mind that makes sense for that?

Will look into replacing the crankcase hoses with proper rubber at some point, I didn’t know this was a thing - as others mentioned, all the vendors sell full silicone kits nowadays so I assumed it was OK. I’ll also peel off that O-ring from the filler neck and see what Napa can do for me. O’Reilly and Autozone never seem to have this kind of thing.

[Ron]

Not significantly from a fueling standpoint as its through the fixed orifice. The free oxygen in the crankcase vapors would be slightly less but it also mingles with the fresh air from the air filter hose. Not to say he shouldn't fix a loose O ring problem but the oily hoses are from the use of silicone.Ah, I didn't catch that he had silicone hoses...had a vision of fumes collecting on them...

Totally agree that the leak is not the problem.

[Ron]

Hey Ron - so I didn’t test the vacuum *inbound* to the solenoid from the valley when the car was cold on the first test. That was my screwup as it left me with no control value for the cold symptoms.

So it seems to me that these connections are good. I’m not sure how to test the distributor as a leak source, do you have a test in mind that makes sense for that?

Will look into replacing the crankcase hoses with proper rubber at some point, I didn’t know this was a thing - as others mentioned, all the vendors sell full silicone kits nowadays so I assumed it was OK. I’ll also peel off that O-ring from the filler neck and see what Napa can do for me. O’Reilly and Autozone never seem to have this kind of thing. A timing light wouldn't tell you unless it was real bad. So, I use a tester similar to this one https://www.enginehones.com/5270.html.
But, you could connect a clean hose to the distributor and manually draw the air out then use your tongue to block it off and see if it holds vacuum...

FWIW- Not only is that all you have left to check vacuum wise in that part of the system. A bad diaphragm in the distributor could easily fit the RPM raising when it warms up. But it probably wouldn't go back down when you hit the throttle every time.

[jawn101]

A timing light wouldn't tell you unless it was real bad. So, I use a tester similar to this one https://www.enginehones.com/5270.html.
But, you could connect a clean hose to the distributor and manually draw the air out then use your tongue to block it off and see if it holds vacuum...

FWIW- Not only is that all you have left to check vacuum wise in that part of the system. A bad diaphragm in the distributor could easily fit the RPM raising when it warms up. But it probably wouldn't go back down when you hit the throttle every time.

Didn’t your mother ever teach you not to pipette by mouth? Was that just me? Scientist parents, lol. Seems reasonable enough, I could give that a shot.

Just a question - I’ve never done a smoke test but is this something that would make leaks obvious? I don’t even know how, though I assume it’s a quick google away.

[Ron]

Didn’t your mother ever teach you not to pipette by mouth? Was that just me? Scientist parents, lol. Seems reasonable enough, I could give that a shot.LOL!
Yeah, but note I said, "you" and "could"!


Just a question - I’ve never done a smoke test but is this something that would make leaks obvious? I don’t even know how, though I assume it’s a quick google away.Smoke might work. But technically, you need to reproduce the same condition as when the suspected problem occurs and sucking is the opposite of blowing. [Don't go there -- It took a lot of self control for me not too... LOL]

[Jonathan]

Oil rated or fuel rated hose will cure the problem. Parts stores will sell PCV rated hose, but you could use oil cooler, trans cooler, or fuel hose too. It just gets more expensive and less flexible if you use fuel/oil hose vs emissions hose.

https://www.instructables.com/id/Why-Silicone-Hoses-Cannot-Be-Used-for-Oil-and-Fuel/

Thanks for that. So it isn't all of the vacuum hose kit hoses that can't be silicone? Just the one(s) directly connected to the oil filler? Could we make a list of which ones shouldn't be silicone (by DMC part number)?

[David T]

A smoke test is where, with the motor off, you pressurize the induction system with smoke. Any tiny leak and you will see wisps of smoke coming out, large leaks and you get a cloud. A smoke test is not a complete end-to-end test of every hose. Any valves in the system can block the smoke. You would have to test each valve and branch of vacuum lines if you suspect leaks past where there are valves. A smoke test can't tell you if valves are not working correctly or if vacuum hoses are not connected correctly. The way I do it I remove the air cleaner box and block off the intake. I connect my smoke to the cold start valve and watch for leaks. The big ones you see quickly and are very obvious, the smaller ones take a bit longer and you have to hunt for them. Vacuum leaks are cumulative, ie, they add up. A bunch of tiny leaks can equal one big leak. Every leak potentially leans the mixture and reduces the control power of the idle system. An induction leak close to an intake valve can lean out a cylinder to the point it can detonate and burn a piston while all the other cylinders are running fine. You should be able to hear the vacuum solenoid on the ignition advance click when you hit idle. If you don't, you have to figure out why you don't. Could be a bad connection, the plug fell off the solenoid, the switch isn't adjusted right, whatever. Very common when working in that tight area in front of the motor, you knock the plug off accidentally and don't realize it. It is also VERY important you have the right hose connected to the right port on that valve. They CANNOT be reversed.

[jawn101]

Hey all, I hope everyone had a great holiday break! I was away for a few days, but am back and thinking about this issue again.

Over the weekend I went and got new o-rings for my oil filler and also enough fuel hose to replace the line between the cap and CSV tube. I still had all the old hose clamps, so it should be very solid. Also, those new O-rings made all the difference - the old ones were very heat damaged and compressed, were making zero content with the filler neck, and were so inflexible I had to cut them off. Now the cap is very snug.

I was playing around a bit with the idle and noticed the behavior in the video below. Basically, when I started the car up, it idled normally (cold). Then I started pressing around on the top of the idle air motor, and noticed that if I put pressure on the electrical connector, the idle changes dramatically. Like, I can rev the engine by doing so. The video speaks volumes on this, it's only 10 seconds long. Just be aware that at the end when the camera is trained on the tach, the only thing I'm doing is putting pressure on the idle speed motor electrical connection - nothing else with the throttle.

https://www.youtube.com/watch?v=JEZbVVOiPfc

I'm guessing this could be related to my issue?

[FABombjoy]

It could be electrical but seems to correlate with pressure which would be atypical. I suspect that pushing on the idle motor is shifting something downstream around.

I'd check & push on the hoses connected to the idle valve / cold start tube and see if any of those have an affect.

[Ron]

You might try watching the valve while pressing and releasing the plug to see if that changes its position...
Or comparing the pressed and released RPM with the unplugged RPM.

[jawn101]

It could be electrical but seems to correlate with pressure which would be atypical. I suspect that pushing on the idle motor is shifting something downstream around.

I'd check & push on the hoses connected to the idle valve / cold start tube and see if any of those have an affect.

It's not a bad theory given how little I show you of what I'm doing, but the idle motor is quite securely attached to the bracket/intake, so to my calibrated arm it feels like I'm only pressing on the electrical connection - though I just noticed there's a hairline crack in the epoxy/potting/whatever around the electrical connector, where it goes into the main motor housing. Maybe that's letting in additional air? I don't know what the internal structure of the motor is like, so no idea if that connector leads into an air chamber or something more isolated.


You might try watching the valve while pressing and releasing the plug to see if that changes its position...
Or comparing the pressed and released RPM with the unplugged RPM.

Ah, interesting. So like just start the car normally and straight up unplug the idle motor?

[Bitsyncmaster]

It's not a bad theory given how little I show you of what I'm doing, but the idle motor is quite securely attached to the bracket/intake, so to my calibrated arm it feels like I'm only pressing on the electrical connection - though I just noticed there's a hairline crack in the epoxy/potting/whatever around the electrical connector, where it goes into the main motor housing. Maybe that's letting in additional air? I don't know what the internal structure of the motor is like, so no idea if that connector leads into an air chamber or something more isolated.

The top electrical part of the idle motor is separated from the lower valve part. Only thing that passes through is a shaft in a bearing. The lower valve assembly has an O-ring sealing it to the outer metal cylinder. So pressing on the connector probably is making or breaking a connection. Most likely in the external connector. Pull the boot off the connector and look for a broken wire at the pins.

[Rich]

.... Most likely in the external connector. Pull the boot off the connector and look for a broken wire at the pins.

Interesting sleuthing that potentially ties the intermittent problem to area at/near the ISM connection point.

Maybe just unplugging/plugging the ISM connector a few times might clean up the internal pins?

ID-ing which wire might be intermittent per Dave's suggestion - try a continuity test between each female contact in the connector and its corresponding pin-socket in the (white 9-pin) bulkhead connector. Pins 4, 8, 9 there.

[Ron]

Ah, interesting. So like just start the car normally and straight up unplug the idle motor?
No (it would probably die), I was thinking just turn the key to Run for a quick comparison/elimination...

+1 Dave and Rich, except it's pins 5, 8, 9.

[jawn101]

Hey folks, sorry for the long, long delay on this thread but wanted to share some new insights for anyone interested. Clint and I checked the car out with a smoke machine today and found three vacuum leaks - injector #5 wasn’t sealing properly (I replaced all the seals and this one seems to just be bad), the ISM pipe, and... the top of the ISM itself, as I suspected. If you remember, I had observed that pressing on the top of the ISM changed the idle characteristics. Well, check out this video.

https://youtu.be/7q_ZVpHPNzI

We temporarily “fixed” it with some superglue and RTV but it’s sloppy and I haven’t come this far to have a literally glued together idle motor :) Off to DeloreanGo with me! Will report back with anything further once I get the replacement injector seal and ISM installed.

I’m also considering Dave M’s solid state idle controller, but that’ll be a phase 2 if anything.

[bytes311]

I discovered I had the same exact leak a month ago. I replaced the stock ISM with a used Volvo unit. The Volvo unit is smaller and runs on less current.

[Elvis]

...

I remember ages ago Elvis was quite hot on the notion of cleaning and maintaining the decel valves on the butterfly plates. I know that these might stick slightly and cause a higher idle.
...


I never talked about these valves. I am always pointing on the complete butterfly assembly which is often not fully closing, especially with vakuum applied.


But seems like you found a new spot for vakuum leaks - good job :-)

[jawn101]

I never talked about these valves. I am always pointing on the complete butterfly assembly which is often not fully closing, especially with vakuum applied.


But seems like you found a new spot for vakuum leaks - good job :-)

Ah, he lives! :) I still think there may be some aspect of the throttle plates not closing completely too, but I’m trying to change as few things as possible at a time to be sure I find the real issue. The ISM was clearly damaged so I’ll drop a new one in and then look for the next problem.


I discovered I had the same exact leak a month ago. I replaced the stock ISM with a used Volvo unit. The Volvo unit is smaller and runs on less current.

Yeah, the one that DeLorean Go sells is much smaller as well. I’m not sure what the crossover point is for it but I’ve come to trust their choices over there, and it was significantly cheaper than a NOS model.

https://www.deloreango.com/us/idle-speed-control-valve-regulator-motor.html

[Chris 16409]

It's best to find a genuine German Bosch Idle Speed Motor. Most usually sell unbranded units. The reliability of these are dubious at best.

64089

[jawn101]

Installed the new idle motor from DeLorean Go today (BTW, those folks are just incredible - they ship to me in CA faster from the UK than Amazon, and there’s an Amazon warehouse in walking distance!) and it’s made a huge difference.

This is the motor they sent, with the old one:https://uploads.tapatalk-cdn.com/20200730/2f67cd5165c7d67c82a7a350997d1500.jpg

And here it is installed:

https://uploads.tapatalk-cdn.com/20200730/30ba11a6a5011d21abb51aec817437c2.jpg

It’s definitely smaller than stock, and looks a little weird because I’m used to the old one, but it works great. Even after a 20 minute drive in the burning 100-degree heat, the idle was a perfect 750 whether the A/C was on or off

https://uploads.tapatalk-cdn.com/20200730/6e41b63e99eb8b19e87e897a84777daa.jpg

But now the issue is the leaky seal around injector #5. That was another obvious vacuum leak when we smoke tested the motor, and even with brand new seals it’s very tenuous. I’ll start another thread for that...