Mitsubishi Repair: Shift to park, idle surge with ac on., simple test, throttle body

Question
Anthony,
Here's one for the books. I have a 00 GT eclipse. The problem is when i come to a stop with the ac is on and you put it in park (automatic) the idle surge's. Not a great deal up and down, it will go low enough at time's the engine shuts-off, does not do it everytime. only when the ac is running. the car has been at the dealer a couple of days to be looked at. when the car was taken in it didn't do it so they kept it to drive. I have not heard anything from them yet. If you have had this problem what was wrong. I have a feeling they want figure it out?
Thanks.  

Answer
Dennis,
My initial guess would be your problem is a malfunctioning Idle Air Control (IAC)  motor.  That is a little motor that allows a measured amount of air to bypass your throttle body plate when it's closed (like when you're at a stop light).  When your A/C is running, the IAC should function more rapidly because there is a bigger strain on the engine. But if the IAC is malfunctioning, it will cause your idle to bounce up and down, and even go low enough to stall out.  If you talk with the dealer mechanics, ask if that has been tested.  It's a pretty simple test they can do even with the car turned off.  
Good luck!