Random Misfire Solved on n54 e90 335i

I was chasing down a random misfire on my car for weeks. It was really starting to get to me. Here were the symptoms:

• All misfires would happen lower in the rev range (idle to around 2k rpm)
• Sometimes it would be just a blip, other times it would be enough to stall the motor (very disconcerting 😠)
• It would happen more when cold, but could still happen randomly even when up to temp
• It would NOT throw a code

The fix

I ordered and installed fresh plugs as a start, as the plugs had been in for a long time (around 50000kms)

When I installed them, and started up the car, I had a PROPER misfire, the car was missing on a cylinder.

I inspected and found that the grounding coil grounding nut was not tight enough.

After I tightened the nut, the problem seemed to be gone!

I still get the odd misfire, but it doesn’t seem to be anywhere near as bad. I have a fresh set of coils on their way to install. I’ll keep you updated!