High Idle / Idle speed motor

[nickcollins]

Hi

My idle speed slowly increases as the car warms up and tops out at about 10000 rpm when hot and cooling fans cut in. I know its not super high but I'm trying to get to the bottom of it, its not throttle linkages or switches. If I disconnect the idle speed motor and apply 12v/ground to the appropriate pins the idle speed motor fully closes and the idle drops to around 800
So my question is, would , under normal circumstances, a fully closed idle speed motor mean that the engine would die through lack of air ? Do I have a vacuum leak of sufficient size to keep the engine running ? Or is it supposed to be fully closed and the signal from the ECU isn't correct ?

Thanks

[Bitsyncmaster]

With the idle motor fully closed the idle RPM should be under 775 RPM. If not the curb idle screw may be holding the throttle plates to far open. Or you may have a vacuum leak (which increases idle speed). Or your ignition vacuum advance is on at idle.

My car did the same (idle at 1000 RPM with warmed up engine). That turned out to be bad deceleration valve springs which created the vacuum leak and increased the the idle RPM.

[nickcollins]

With the idle motor fully closed the idle RPM should be under 775 RPM. If not the curb idle screw may be holding the throttle plates to far open. Or you may have a vacuum leak (which increases idle speed). Or your ignition vacuum advance is on at idle.

My car did the same (idle at 1000 RPM with warmed up engine). That turned out to be bad deceleration valve springs which created the vacuum leak and increased the the idle RPM.


Its not the curb idle screw and its not advancing the ignition on idle ( pulled the pipe ) so its either vacuum leak or the springs.I'm going to have a look at the springs tonight and have ordered a set of vacuum tubes and injector seals.

[nickcollins]

52899
With the idle motor fully closed the idle RPM should be under 775 RPM. If not the curb idle screw may be holding the throttle plates to far open. Or you may have a vacuum leak (which increases idle speed). Or your ignition vacuum advance is on at idle.

My car did the same (idle at 1000 RPM with warmed up engine). That turned out to be bad deceleration valve springs which created the vacuum leak and increased the the idle RPM.



Are these the deceleration springs and are these bad ?

[David T]

52899



Are these the deceleration springs and are these bad ?

Yes and yes.

[nickcollins]

Thanks and damn, no stock at Delorean . Anyone know where to get one from ?

And which order is it for the plastic ring and o ring ? The parts catalogue pic seems to indicate o ring closest to w pipe but mine had the plastic ring first , then the o ring ??

Thank you

[kings1527]

I had the exact same issue and here's what mine looked like before and then with the NOS when they were still available. There was definitely a bad batch of deceleration springs out there that caused high idle issues. They had the NOS throttle bodies up until maybe a couple years ago. They were around $62 then went to $87 and then NLA. Not that any of that matters now. I'd imagine one of the dealers has a nice used one with good springs lying around.

5290152900

[Bitsyncmaster]

Thanks and damn, no stock at Delorean . Anyone know where to get one from ?

And which order is it for the plastic ring and o ring ? The parts catalogue pic seems to indicate o ring closest to w pipe but mine had the plastic ring first , then the o ring ??

Thank you

Yes you have the bad springs. There are a few throttle bodys that show up from time to time from owners converting to EFI. That is where I got my good throttle body.

[David T]

You could use the springs that you can get in an ink pen. Might have to cut them a little shorter.

[nickcollins]

Yes you have the bad springs. There are a few throttle bodys that show up from time to time from owners converting to EFI. That is where I got my good throttle body.


Thanks for the help. Hopefully someone can confirm the order of o ring and plastic ring on the w pipe as i have to put it back together. Guess I'm stuck with a high idle until a good one turns up somewhere.
Do you think this type of leak would affect my exhaust emissions ? I failed CA smog recently and was looking for air leaks that might contribute to the high NOx measurements I got

[NckT]

You could always solder them shut.

[David T]

You could always solder them shut.

That would be OK on an automatic but you really do need them for the 5-speed.

[Bitsyncmaster]

Thanks for the help. Hopefully someone can confirm the order of o ring and plastic ring on the w pipe as i have to put it back together. Guess I'm stuck with a high idle until a good one turns up somewhere.
Do you think this type of leak would affect my exhaust emissions ? I failed CA smog recently and was looking for air leaks that might contribute to the high NOx measurements I got

I don't think the springs would affect emissions unless the higher idle speed affected emissions.

By the way I tried to run with the bad set of springs removed and bolted the holes closed. Car would run OK but when you took you foot off the gas not in gear the engine RPM would really drop to low (about 500 RPM). I tried some software changes in my idle ECU which helped but it still would happen sometimes. So I went back to a used throttle assembly with good springs.

[nickcollins]

[QUOTE=Bitsyncmaster;223430]I don't think the springs would affect emissions unless the higher idle speed affected emissions.



More air means a higher NOx reading, or so i'm told

[Bitsyncmaster]

[QUOTE=Bitsyncmaster;223430]I don't think the springs would affect emissions unless the higher idle speed affected emissions.



More air means a higher NOx reading, or so i'm told

I would think if the lambda is running the mixture is correct at 14.7 AFR. The more air just results in higher RPM. The lambda works at all RPM except when wide open throttle.

[nickcollins]

[QUOTE=nickcollins;223434]

I would think if the lambda is running the mixture is correct at 14.7 AFR. The more air just results in higher RPM. The lambda works at all RPM except when wide open throttle.


Sounds right to me, more air so the system adds more fuel to keep the ratio hence a higher rpm
I was told that my failed NOx was possibly due to a vacuum leak which also gave me a high rpm so I've been hunting for a leak for a while now.

[David T]

The decel springs (and valves) were meant to reduce emissions during deceleration. It would allow the mixture to lean out so you would get less hydrocarbons. It also makes the ride a bit softer. Not really necessary on an automatic, the torque converter can handle it. Odd thing about the Delorean. The motor is set up exactly the same for the auto and the 5-speed. Usually you see the idle, timing, and advance set up a little differently on a 5-speed vs an automatic, but not on a Delorean! I guess they didn't make as many autos so they didn't have to do emissions testing on them so they didn't tweak them.

[NckT]

That would be OK on an automatic but you really do need them for the 5-speed.

I disagree. I understand what the purpose is for these air admittance valves, but you can remove them in their entirety by replacing the throttle discs or solder them shut. They only open when the throttle is shut and the car is on the over run.

I've set up a few Deloreans with oem no dec valve throttle discs and it has had no adverse effect on the engine running on deceleration at all. I've done this on many other non k jet cars also.