CEL = P0505 = Idle Air Control Motor (IAC) circuit condition or idle speed higher/lower than expected.

Definition: IAC circuit condition or idle speed higher/lower than expected.

Explanation: The ECM has detected that the IAC counts are higher or lower than expected, the engine speed is not its expected range.

Probable causes:
1- Vacuum leak on the engine
2- Dirty throttle body
3- IAC motor is defetive
4- Poor electrical connection to the IAC valve.

I got this after install the catch can (I removed the throttle body and manifolds). Went back unplugged, and re-plugged everything, checked for boost leaks, made sure everything is seated properly, and checked the tightness of all of the screws. Reset the code by unplugging the battery and I haven't got it since (300miles ago). IMHO I'd start there. Good Luck. -Steve