check the wiring to the iac valve and check the unit it'self to make sure the bolts that hold it in didn't un tq themselves and create a gap for air to leak out . it's on the back of the intake manifold and it's bolted in by 2 12mm head size bolts I believe.
I'm with you two on this one, it sounds like a problem with the IAC valve.if the iacv is dirty or not functioning properly it will cause the idle to be like that, check the wiring to it and then take it off and inspect/clean it and re install. If you still have the same problem buy a new one