Idle Air Control valve

[RiCe_KiLlEr]

i have been having some idling issues after my new engine install and the installation of my supercharger. my car was idling high so i went and got a new IAC valve. after i installed it that the idle dropped to around 950-1000rpms. while driving the car wants to keep the rpms around 2k. if i am coming to a stop i put the car in neutral and coast. the idle will stay around 2k until i come to a complete stop and wait 5-10 seconds. after that the idle would drop to around 1000rpms. so i went and disconnected the the plug on the IAC valve and the car idles normal and i no longer have the idle hanging around 2k while driving. it is back to normal. if i plug the IAC valve it goes back to doing what it was. i am confused and have no clue whats wrong. it throws a code though while unplugged. code says IAC circuit or something like that. any ideas? id appreciate all the help. i also replaced the TPS sensor and same thing

 

[01yellercobra]

If it only does it while the IAC is plugged in then the tune probably needs to be tweaked.