1992 Honda Prelude Rough short term idle when starting

Everyday when I go out to the car for the first time, or it sits for a while, and I start it, it idles really rough like it's not getting much gas or a few cylinders aren't working and it SEEMS like it would die. But after about 10-15 seconds it starts idling perfectly. If I shut it of and restart it, it's fine. It only happens when it's a cold engine. It happens in either hot or cold weather. I have replaced the plugs, wires, rotor, cap, thermal control valve, used fuel injector cleaner. Can't think of anything else that would cause such a short term problem. Thanks in advance.