Thread: Misfire only at idle on #2

After L32 swap into my GT, I'm getting a crap load of misfires only on #2 and only at idle. I get up to 200 misfires (using aeroforce gauge) while idling and once under load while driving misfires go to 0 and misfires return when back to idle. When motor is warm--it still happens, but amount of misfires appear to go down. Swapped out plug (looked fine-not wet), wire, coil and injector-- no help. Vacuum is steady at 19-20, motor has about 50 k on it and didn't do this before swap--but motor sat for about 4 months (may-sept) in donor car. Took it out on hwy for over an hour-running the piss out of it hoping to get it hot enough to cure it--no luck. So question is...why only at idle? Would a valve issue not misfire all the time? Could a pitted cam lobe cause this? Head gasket? Any ideas out there?

Start with the basics:
Possible causes

- Faulty spark plug 2
- Clogged or faulty fuel injector 2
- Faulty ignition coil 2
- Fuel injector 2 harness is open or shorted
- Fuel injector 2 circuit poor electrical connection
- Ignition coil 2 harness is open or shorted
- Ignition coil 2 circuit poor electrical connection
- Insufficient cylinder 2 compression
- Incorrect fuel pressure
- Intake air leak

and make sure your MAF is good.

Originally Posted by Explicit_Spade

Start with the basics:
Possible causes

- Faulty spark plug 2
- Clogged or faulty fuel injector 2
- Faulty ignition coil 2
- Fuel injector 2 harness is open or shorted
- Fuel injector 2 circuit poor electrical connection
- Ignition coil 2 harness is open or shorted
- Ignition coil 2 circuit poor electrical connection
- Insufficient cylinder 2 compression
- Incorrect fuel pressure
- Intake air leak

and make sure your MAF is good.

Like I said, I've already swapped out all the parts with known good parts and I've checked the connections- they appear to be clean and making good contact. I can't hear or find any leaks. One thing I forgot to mention is that when I started it up for first time since install, after a minute or 2 engine started making somewhat loud ticking noises. (didn't have oil gauge hooked up yet--dumb move) so I shut it off and checked dip stick-- didn't look like oil hadn't moved much so I banged on oil pump housing thinking that spring might of been stuck after sitting for a while. Restarted it and noise went away and now dip stick was wet. Engine appeared to run fine after that-- no noise or smoke. After gauge install, pressure is 60 at load and about 45 idle--seems good. So possible temporary oil starvation causing damage to cam lobe or rings? Haven't done compression test yet, but performance doesn't seem an issue- car is pulling hard with no problems.

Also...can a faulty MAF cause misfires to only one cylinder?

Originally Posted by sugaryuk

Also...can a faulty MAF cause misfires to only one cylinder?

As strange as it sounds, it has happened. There's a several page thread somewhere on here where someone was troubleshooting a cylinder 2 misfire and a new MAF fixed the problem.


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Originally Posted by nox

IIRC just unplug the MAF it should go to base tables, that should help diagnose it. You didn't mention if you did a compression test on Cylinder 2. A minor leak or tear could cause idle issues that go away under acceleration. How do you know the coil is good or the ICM is?

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I'll try unplugging the MAF to rule it out. Haven't done a compression test yet--no tester...probably be my next purchase. I swapped 2/5 coil with 3/6 (which wasn't showing any misfires) and the misfires stayed on #2 cylinder. Haven't swapped the ICM out yet but I have a spare GT ICM--know if they are interchangeable? Like you mentioned, starting to think I might have a leak, possibly intake related?