My engine is idling at 1500 rpm in Park. I've looked for a vacuum leak and also had a mechanic check it with no luck. I installed a Performance Products 52mm throttle body and just replaced the iac valve. Any suggestions?

 

Assuming there is no vacuum leak, you need to do a base idle adjustment since you changed the TB. Search for those key words and you'll find the procedure.

 

I'd go along with what Matatk said other than to follow the usual procedure. The procedure is simple, easy and requires no tools. It also will ASSUME that there is no leak (just becuase you can't find it doesn't mean there isn't one), the desired RPM per the ECM is stock, your tach is right and nothing else is reporting wrong data. Set it with a scanner.