Idle problem.

[SamE30e]

Ok, So heres my problem

I start my car and it automatically revs to about 3500 rpm and sits there for like 10-20 seconds, then it drops down to 1000 and bounces from 1000 - 1500.

Unplugging the ICM doesn't do anything and neither does unplugging the throttle control servo at the bottom of the TB..

I'm thinking the ICM is shot. Does this make sense?

[DaveSmed]

Ok, So heres my problem

I start my car and it automatically revs to about 3500 rpm and sits there for like 10-20 seconds, then it drops down to 1000 and bounces from 1000 - 1500.

Unplugging the ICM doesn't do anything and neither does unplugging the throttle control servo at the bottom of the TB..

I'm thinking the ICM is shot. Does this make sense?

Your most likely correct. Don't know what you unplugged at the bottom of the TB though, your IAC should be over your valve cover on a bracket IIRC

Pop the ICM out and open it up (it can be a pain in the ass) Bet you will find a very obviously roasted transistor confirming diagnosis.

[SamE30e]

I think it might be the ICV. I plugged the hose going to the elbow before the tb and the rev's dropped. So temporarily I clamped a mini pair of vice grips to plug the line partially and it idles properly now.

Would that make it the ICV?

[DaveSmed]

Not necessarily. It should default to a wide open position.

I forget the exact number, but motronic has a very low rev limiter for when the idle switch is closed. That hunting idle is actually a rev limiter bounce. That shows that your idle switch in your TPS is working, so your ICM and IAC SHOULD be controlling your idle. Etas are known for failures at the ICM, due to improper cooling of the transistor that controls current to the IAC. There have been updated modules (I think they have a stripe or something?) that add a more substantial heatsink to it.

I bet if you pull yours, you'll see a charred transistor.

[Court M3]

OT but does anyone know if the early euro models come with an ICM?

[SamE30e]

Mines a green ICM no stripe though. I assume I need a new one.

[SamE30e]

Until my car warms up I have to stay on the gas lol, pain in the ass man.

[DaveSmed]

Mines a green ICM no stripe though. I assume I need a new one.

Got me. I always checked by taking them apart. It was pretty obvious at that point what the issue was.


As far as early vs. late, no idea. Got an engine bay pic?

[SamE30e]

I might pull mine apart and check it, right now it's alright when the cars warm but its a bitch to get started.

[DaveSmed]

Starts perfect when you hold the throttle open a bit though, right? if not check out your thermo-time switch and 7th injector