I have a 96 gt mustang, and I just recently installed the slp LM exhaust system..its been running real good. But everytime after I'm done driving and I come to a stop and put the car in park and wait a sec, the idle rpm drops real low and almost shuts off, it has shut off a couple times before..What is causing this?

It doesn't do this when I drive around and stop at a stop light.

 

try cleaning your IAC, that worked for me

http://www.muscularmustangs.com/iac.php