I'm sorry to say that I have had the same issue. Replaced the IAC with a new one but could not the gasket on. (major mistake). now when i start the car it revs way too high for like 5 minutes and then comes to a normal idle. But the thing is messed up because it accelerates on its own at 40 mph with my foot off the gas.
I will remove this IAC and put the gasket on like i should have. According to the experts/moderators on this site, a vacuum leak around the gasket can be the cause. Since all i fooled with was the IAC (plus cleaning TB) it appears the gasket (lack-of) is implicated.
I'll report back whhat happens with the new gasket.