AJ1990

I have a 06 reg cab colorado with a ls2/4l65e out of an 06 gto. I'm having an issue when I plug in the A/C pressure switch it goes into "reduced power mode and gives me a P2138 code. I do have have a high idle around 1100-1200 when hot and there is a slight high pitched noice coming from the throttle body when the truck is turned off. Could it be a bad throttle body? I've checked for vacuum leaks and everything is good. Any help would be greatly appreciated