My idle is kind of wonky. 1000rpms for 2 seconds, then 500 rpms, then it will soar down to like 100rpms, and almost dies.

What would it be? vaccuum leak? How would I check for that?

Car has almost full bolt ons., and just got an American Muscle tune.

I also threw two codes last night, p1000, and a p0430. The p1000 is a learning code I believe, and the p0430 is a catalyst system code. I don't have cats but I told the guy at AM to tune them out. He probably forgot.

 

Could try the IAC valve, had that happen to me and this fixed it.