Idle issue getting me confused

[bimmerpirate]

I've got an 07/85 m10 that is giving me some trouble trying to fix the idle issue. When starting up, it runs up to about 2300rpm for a few moments then starts reving from 500-1300rpm. I've already replaced most of the vacuum hoses already and done a bunch of troubleshooting but i'm stumped.


tested so far:

If i connect direct 12 volts from the battery, the ICV closes and it idles normally
ICV voltage: 12.8v
ICV resistance: 10ohms
ICV current: 43mA
ICV does not activate when the car runs. no humming or vibrations felt from it.

Not really sure what to test from here or what might be the problem.

Thanks in advance.

[TobyB]

Air leaks. Take the boot off and give it a good rolfing. If it comes apart, replace it.

hth

t

[bimmerpirate]

not air leaks. I've replaced every single vac line, boot and hose.

[thebutterson]

Sounds like most of the other cars here. If you're sure there aren't vacuum leaks you can either deal with it or look at replacing the ICV or idle computer. If you look at the previous posts in the m10 forum quite a few of them are idle related.

[PimpinWalrus]

I had the same problem for the past 3 months and fixed it yesterday. Try the penny trick. Remove your ICV and give it a good cleaning with Carb Cleaner. Drill 1/4 hole in a penny and place it on the intake side (Hose from the intake manifold side) of the ICV. From here the adjuster screw on the top of the ICV was actually functioning for once. Start screwing in the adjuster and the revs should start to even out until you get a balanced idle around 800. If it starts reving again keep adjusting.

[Deadskittles]

1: Remove ICV
2: Throw away ICV
3: ????????
4: Profit

[KI4UJO]

While tossing the ICV sounds like a good idea, just remember that BMW built the M10 to idle properly. It still can. I'll admit, mine doesn't idle right. However, I now know what is wrong and am working to solve the problem.

As for yours, check the throttle position sensor (TPS). It has three pins. Check it from the center pin to each side. It should have continuity from the center pin to one side when the throttle body is closed, and continuity from the center to the other side at wide open throttle. The TPS is known to cause surging issues on the M10.

Assuming that you have the bentley, it gives pinouts to check at the DME and Idle Control Module connectors. This is worth your time, as you can have good sensors but have a wiring fault. If your ICV is not making any noise or doing anything while the car is running, you definitely have a problem. Even with my problems (described below), the ICV has never lost signal.

Also, have you had a smoke test run? Like you, I replaced every single hose - only to determine that my throttle body, distributor, and charcoal canister were creating leaks. It is really the only way to know that the system is 100% leak free.

PM me if you need any more info. I have a large amount of info on L-jet and how it works, what it needs to operate properly, etc.

[bimmerpirate]

I think i fixed it finally?

while trying the drilled penny idea, i noticed that the one vac line for the idle advance (which i didnt replace yet) was a bit cracked, so i replaced it afterwards and between the two, now it idles at about 500-600rpm. I kinda dont want to mess with it now to see if it works without the penny. If it's not broke anymore, dont fix it, right?

[Acet]

isnt 500-600 a low idle?

[Acet]

Well I deleted the ICV today with all of the plumbing (eliminated unnecessary possibilities of vac leaks). Car idles and drives great!

Extra plumbing:


Intake mani plug:


Solid idle at 800rpms



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