I have a 1986 Camaro IROC Z LB9 and a couple of days ago a rough idle appeared during cold starts. Basically my car will start, RPMs will shoot up to 1000 and quickly drop below 500. The engine will want to stall and I have to rev it to keep it alive. But time I back of the driveway and get down the street, the engine is warm and the car is fine. However, when I start the car again after driving it starts fine! This problem only appears after cold starts when the car has been sitting for several hours.

Last time my car did this was last year and I replaced the EGR exactly 11 months ago. A few days ago I replaced the PCV valve and it was the original unit (AC Spark Plugs) and after replacing it my idle became even smoother. Two days ago I replaced my Coolant Temperature Sender (the Driver's side head) and the next morning is when the rough idle returned. Could it be related to that?

MAF sensor was replaced 3 years ago, along with the ECM, As far as I know every Vacuum line was replaced about 4 years ago. Fuel system was fully rebuilt a couple of years ago (New fuel pump, sending unit, fuel filter and fuel pressure regulator).

I was planning on replacing the IAC valve, I'm guessing it can't hurt at this point. Could it be the IAC valve finally crapped out? Anything else I should replace as caution?