Alright so i have a 98 z24 cavalier standard. For some time now my when started from a cold start or anything longer then an hour it has a rough idle with rpm's fluxuating almost to a stall and then all of a sudden the engine corrects itself to a nice smooth idle. No code comes up and i have replaced O2 sensor, plugs with ac delco's. This one is odd because after the 10 seconds it takes to smooth out its almost like nothing ever happened acceleration is perfect it almost idles perfect with a very minor miss. I need some help

 

Personally,I would clean the throttle body first.You would be amazed at the gunk that builds up before,and after the throttle plate.Pull the ducting off,and look at it with a flashlight,open the throttle plate,and see whats behind it.Sounds like to me like you probably have a plugged up port.

 

could check your iac valve to may need to be cleaned.

 

Yes, it sounds like the IAC valve, which often gets quite dirty. Easy to clean, though, two torx bolts at back of TB.