My GTA developed a terrible stumble to it yesterday. When the engine is cold/not been at operating temp for a min or 2, when I’m coming to a stop the car starts idling down at around 400rpm, and then will either rev up and start idling normally, or die. I’m not even really sure where to start looking. When the car is at operating temp, the iac is around 35 in gear. Tps is set currently to .60, was originally at .67 since that is what was requested from pcm for less for the chip I have.

maf readings at idle in gear look good, 6-7, it’s not running lean, infact running a little rich from the 24# injectors and it’s pulling it back, but again, those injectors have been in the car for almost a year now, I have good fuel pressure. 37-40 idle ish and 47-50 no vacuum, egr disconnected.

when it starts stumbling, I can actually hear, and watch on my scantool and see the idle air control opening up all the way, the car keeps running like crap for a couple seconds and then just starts to idle fine and the iac comes down

all I can think is it’s a timing related problem, or maybe knock sensor?? But it only does it at idle, and the car still seems to make good power.