Just wanted to let everyone know that there is now a fix for your hanging RPM problems. It's a plate that goes between the IAC valve. People have used it and they say it helps out a TON. For more info go to the link below. I just ordered mine today!!
http://www.mach1registry.org/forums/showthread.php?s=&threadid=20268
http://www.mach1registry.org/forums/showthread.php?s=&threadid=20268