91 camaro RS 305 TBI 5 speed, 80% of the time the car starts and idles at a perfectly regular, perfectly smooth idle speed. standard 1-2 second start up time, flawless. After i drive it a little, turn it off for under an hour, and start it back up, it seems to start immediately, like within the first half second, and the idle climbs to 1500-2000 and holds at that speed as if it thinks that that is its regular idle speed. shutting it off and restarting solves the issue, but takes 3-5 seconds of turning over for it to get ignition. Any ideas guys?

 

Anyone?

 

Most likely the IAC motor is going bad or the worm gear is worn. During cranking the ecm usually commands the IAC to open up much more than is needed for your idle speed and then it tapers it down to a much smaller value. If the valve is stuck, dirty, going bad or worn it may get stuck at a certain position and cause a high idle. As for the harder to start it could be that it is in a closed or nearly closed position when the engine is shut off and when the ecm wants to enter cranking mode it sends a signal for the IAC motor to open up but it cant/doesn't. So you are cranking and spraying more fuel than is needed for the smaller amount of air entering so when you tip in the throttle you are letting in more air which corrects the rich condition.