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]

0821171841a.jpg

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]

0821171841a.jpg



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.

IMG_4175.jpgIMG_4311.jpg

[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