Check the electrical connections on the IAC valve.
Also, it might be worth removing the throttle body and giving it a good cleaning. They can collect carbon and grunge, which will cause an erratic idle. You'll need to remove the IAC from the throttle body and make sure that all the passages are clean. (After removing the IAC, then remove the throttle body from the engine. You'll need a bunch of leverage to get the IAC to come loose.)
I think that the last time I cleaned mine, I used Brake Parts Cleaner or lacquer thinner. (Try them both. See which one works better.)
Be careful if you spray the parts cleaner into any of the little orifices in the TB. Some of them just loop around to the same side, and will direct the spray back into your face. Don't ask how I know this.

Don't let any solvent get into the TPS. I understand they don't like that.