I thought I would bring this out of the MS section so that I could get more ideas thrown my way. Here is the original thread with a MS log.
idle perfect, then suddenly full rich on afr
It is completely random. Sometimes it takes a couple minutes, and other times it will do it one after the other. I replaced the COPs and it still happens. It occurs during idle, and while driving under load. After replacing the COPs it did seem like the frequency decreased, but could be my imagination. I orders a set of NGK 4091 spark plugs. The plugs seem normal. I'm wondering if a plug is grounding out. Usually it is obvious if the plug is grounding to the head because you will see black on the insulator. I had what felt like a misfire occasional while driving when the diypnp was hooked up. Now with the MS3 it is very pronounced. However, my idle is sooooo stable with the MS3, that any hicuup is obvious.
The car is idling smoothly and then suddenly stumbles. AFR goes full rich for about 1.5 - 2s before it recovers and continues to idle fine.
I read a thread where an injector harness had rubbed to a point where an injector wire was grounding on the head causing excess fuel to be dumped. I moved the harness and still had the stumbles.
If the new plugs don't fix it, then I'm at a loss.
I watched the trigger log and when it stumbled the y axis (ms) increased, but I assume that is because the engine slowed down. I tried to log the trigger, but it won't record long enough to get the stumble.
I'm running seq. spark and fuel.