Got a high idle problem.
 

2002 v6 auto. The car ran fine when i left Pittsburgh this morning, about 100 miles later we stopped to get something to eat. When we stopped in the parking spot, the car was at about 800RPM then shifted from drive to park and the car jumped to about 1500 an slowly went down to about 1100 and stayed there. No CEL, and besides that the car runs fine. I'm gonna let the car cool down and and start it up tomorrow and see what happens and i'll probably run some throttle body cleaner this weekend and maybe clean up the TPS. Any other ideas? They would be much appreciated.

IAC? That is the only other thing that could really cause an issue.

Yours sounds like it has more to do with a vacuum type of issue if it only does it when its in park..

Ya look for a vacuum leak. That's what it sounds like to me.

Well i used a modis and the IAC is moving but wont shut pass 50 percent, however, if i press the brakes the engine revs up a bit each pump so im leaning towards a vacuum leak at the booster. I'll look into it tomorrow when i have more time.

I had a similar problem and it ended up being a faulty throttle position sensor. It'd idle around 800-1200 and sometimes when I would give it throttle and then let off, it would stick at a higher rpm like 2000.

Fixed, weirdly, but its idling normal again. A buddy of mine, Ben, a.k.a. The German, is a Mustang expert. His claim was that the ECU was compensating for the lack of back pressure from glasspack i put on well over a year ago, so all we did was disconnect the battery and reset the computer and now shes running like a goddamned champ.