Another intermittent misfire :hitler:

[damastah]

So I have what everyone gets once in their e30 lifetime... A freaking intermittent misfire.

Currently, the car ALWAYS misfires at idle. The intervals between the misfires could be 2 or 3 times in the same fire cycle, or it could go a good 15 seconds between misfires.

When driving, it will not misfire when driving for longer than 30 minutes and it's warmed up all the way. It will misfire when cold and just like a flick of a switch it will drive 100% normal. I will floor it to redline, not a single misfire; only at idle.


I saw valve cover was leaking and previous plugs had oil, so I changed the gasket and the plugs hoping that would fix it, however it is still misfiring.

I took it to the shop, the fixed the small vacuum leak I had, and checked ECU, and spark and fuel and the mechanic says it's fine.

I'm thinking AFM because it can go from driving horribly and just a flick of the switch drives perfectly fine except for the occasional idle misfire.

What are your thoughts? Is there anything I should do/check in particular?

Thanks

[PandaRed30]

I have the exact same issue... Trying to find a fix now just hoping someone know something.

[e30onBBSs]

Isolate the cylinder it's on by doing a power balance test. Usually they don't jump around randomly. Pull a plug wire from cylinder 1 and see what happens. Obviously it will run kinda shittily but maybe it will still obviously misfire somewhere else. Proceed through all the plugs and see what happens. It might not show you anything because the resolution of the misfire may be disturbed by the test but I would start there then proceed with diagnosis.

[dnguyen1963]

Isolate the cylinder it's on by doing a power balance test. Usually they don't jump around randomly. Pull a plug wire from cylinder 1 and see what happens. Obviously it will run kinda shittily but maybe it will still obviously misfire somewhere else. Proceed through all the plugs and see what happens. It might not show you anything because the resolution of the misfire may be disturbed by the test but I would start there then proceed with diagnosis.

You can use a stethoscope to listen. Often time, the misfire can be heard doing it this way instead of remove the plug wire.