LQ1 misfires at idle

[RacerX]

My car, a 1996 Z34 with the LQ1, keeps getting a misfire on cylinder #4. Originally, assuming this is purely an ignition problem, I went after the plugs, wires and coils. I have been able to eliminate sporadic powerloss and a tendency to buck at low rpm with the TC locked, but a misfire at idle persists with a code pointing to cylinder #4. Got any ideas?

[White93z34]

did you replace the ICM with the coils as well?

 

i take it when driving it smooths out?

[RacerX]

The ICM is still original, and the idle does eventually become smoother after about an hour of driving it.

 

 

EDIT: I find it strange that when it gets bad enough to actually set the SES light, the idle suddenly becomes smoother.

[GP1138]

The ICM is still original, and the idle does eventually become smoother after about an hour of driving it.

 

 

EDIT: I find it strange that when it gets bad enough to actually set the SES light, the idle suddenly becomes smoother.

 

If the SES light comes on, the computer might be retarding the timing or something to reduce misfires.. I think that's how it works.

[Crimson Fury Z]

take it from me, replace the icm, i had to hit the gas hard at start up to even get a code. mainly if it isn't bad, it wont throw it. don't delay like i did and get stranded .

[GOT2B GM]

I would take the ICM out and take it to your local parts store and get it tested. Here in Canada, we have PartSource and they test them for free. That way you know for sure if its your problem.

[Crimson Fury Z]

yes! forgot about having it tested. make it so RacerX

[RacerX]

Is it likely for the ICM to malfunction only at idle and have no impact on performance?

[Guest Anonymous]

My old 3.4 does this...