• The site migration is complete! Hopefully everything transferred properly from the multiple decades old software we were using before. If you notice any issues please let me know, thanks! Also, I'm still working on things like chatbox, etc so hopefully those will be working in the next week or two.

Chasing a rough idle

The ICM is the Idle Control Motor? Is that the other thing with a wiring harness going to it other than the MAF? Is held on by 2 screws and looks like a bullet shaped plunger that mates to a similarly shaped profile in the TB? If that's what we're talking about, I took it out and cleaned up the chamber but did not replace the part. Are you saying it could be shot altogether? Any way to test it?
 


That would be your IAC, idle air control. ICM is thr ignition control module. It sits under the coils, and a pigtail from the wire harness bolts to it.

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Not really.

They can test perfect and still be bad. A good test is to "borrow" one from a friends car if they so happen to own a car with a 3800 and see what your car does.
 
Are there any other symptoms besides a rough idle? I'm not really having any drivability issues. I suppose I could swap the 98 with the 01 and see if it helps.

One thing I've noticed is that the idle is fine at start up and the engine is cold. It's only after driving and it comes up to temp that the idle gets rough.
 
I'm having a very similar shudder in the idle but in a series III motor. It only shows at idle in park or nuetral, it does not occur in when in gear, and no shortage of power or problems under acceleration. I've replaced air filter, new iridium NGK plugs and new wires. How many of the potential solutions in this thread apply to the Series III? Sorry if I'm thread jacking!

Last night when I was dinking around I noticed with the cabin fan OFF it was much more noticeable as the RPMs dropped to a consistent 600...

Thanks guys.
 


For the Series III I'd remove and clean the TB, and possibly change the IAC valve. The TB on the 04+'s like to give issues when they get too much carbon built up on them. Before you do that, may want to try cleaning your MAF sensor as well.
 
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