Could be a few things. You're idle fluxing and you're getting cold air with your heat on.....Interesting.

Could be the IAC (Idle Air Control) Valve like you said. Have you checked the cooling system yet? You just have some air in system, that could account for the funky idle. If you didn't have enough water in the system at all, you won't get hot air out of the heater either.

How high did your temp gauge get? Was it way up like overheating or just in the normal range.