Thread: ICM Problems??

Could a bad ICM cause a rough Idle, but not cause problems elsewhere? Cause I've eliminated most other options, and before I go invest in a new ICM I'd like opinions if it could f-up the idle only.

The car runs fine at any engine speed above 1300 rpm, in the 900 - 1250 rpm range there is a slight miss, and at idle it is rough, sometimes even stalling out, new plugs, swapped out the coils for a new one, no change... eliminated all other options than a bad ICM or possibly a screwed up PCM

I dunno, the ICM would not be my first thought in that. Its not unheard of that they go bad, but its not all that common either.

Dont get me wrong, its entirely possible, but with a rough idle and stalling, I would be looking more in the direction of the IAC, MAF, that sorta thing. Just because you didnt mention it, and because you've changed the plugs and coils, might be worth looking at the plug wires. Though even those wouldnt pop to the top of my list.

Are there any codes, SES light on or flashing or anything like that?

Ive tried all sensors and none are causing the problem, I have no ses light,(other than when I was checking sensors) I am running out of ideas on what it could be hence why I'm looking at icm, Like if it has an idle circuit in it or something that is bad.... but now that I think of it,a open in a spark plug wire may cause this... but it isnt constant.... this one is a real head scratcher

I'll give you a call this week if I need and thanks for the offer schlim

Yeah, the cables have less than 8k as did the plugs, but plugs were cheap, and old ones were a heat range colder and with all my short trips got pretty fouled

Well, swapped the ICM, no change.... now time for wires, This is becoming such a headache

Just a note, don't just swap the coils, the third contact on these dual-coil HV "ignition coils" is the washer under the screw between the two spade contacts and that passenger side screw! Make certain that screw is in like new and rustless condition and ALSO that the HV/ICM mounting base and mounting platform (also the passenger side engine mount on the engine and a wonderful ICM-baking grill) has never loosened or rusted from the cylinder head!

On my 2000 GTP (200K) I just noticed the other day that when trying to use the passenger engine mount/ICM platform (chain hole) as a ground for boosting a dead battery, it was not accepted as a legit battery ground, though the engine block was! It had over 3 Ω of resistance due no doubt to rust causing poor electrical conductivity between it and the head/block!

This may even be the source of the odd CPS failures, coupled with salt corrosion on the ICM's own heatsink/baseplate ground, I know a few ohms isn't much, but when we are talking about 50KV we are talking major spikes into/across the third longest end tail (digital) ground loop of the engine harness. These coils generate far more and odder square wave wideband "spike" harmonics and also more voltage at lower switching frequencies than when buzzing along, perhaps even enough to cause other electronic sensor-related problems