Random misfires at idle. I'm stumped!
Hello all! Got a problem and I'm having a serious blond moment lately trying to figure this one out. I'm working on my buddy's 06 GTO, automatic transmission, only mods are a K&N Filter and a straight pipe exhaust.
When it's sitting at idle, warm or cold, the car "bumps," enough to be felt lightly through the whole car. I'd say it's a misfire as it certainly feels like it. It happens in an irregular cycle between every 2-9 seconds.
Thinking he had fouled spark plus, I had him go buy Bosch 4-tine Iridiums, I've had good luck with them. I check the wires upon removing them and they looked fine, the plugs looked in good shape with a very slight white frosting, which I'm guessing maybe it's running hot or lean. He has a new battery, I haven't checked his coils yet, and I'm thinking I'm seriously missing something. He says he hasn't noticed any loss of performance or anything.
I'm really thinking my fiancee clubbed me in the middle of the night and I'm sitting a few fries short of a happy meal, but I'm currently stumped and need help for my buddy. He's thinking his car is in full rebellion against him and he's about to use it as a mobile target. Any help would be appreciated, thanks greatly!
By the way, any jokes as far as my own brain misfiring at idle as this should be an easy fix, are always appreciated.