Probably just need to clean the throttle body. Get some throttle body cleaner (spray can),NOT CARB. CLEANER, engine off, open throttle body, spray cleaner on a rag,wipe down the walls of the throttle body, and BOTH sides of the throttle plate espcially where the two parts meet! The last part sounds hard, but it's not - stick a finger in a rag, next to edgeworks best, spray it with cleaner (really wet it down), used the finger and rag while playing with the throttle valve,or throttle plate if you will, till all the black CRAP is gone. Your idle air control ( IAC Motor) knows what that gap SHOULD BE it was programmed that the opening between the plate a wall would X, it also knows where the throttle plate SHOULD BE (TPS switch tells it) if the TPS says it is OK but the Crap blocks the air passage around the throttle plate and the throttle wall the computer doesn't care it's not programmed to fix this and may not even set a code for it either. Engine can not idle without fuel and AIR. Sometime it will all of a sudden idle if ya turn the air on cause the computer was told a/c on raise idle! Computers are smart (depending on what info it was taught) but BLIND AS A BAT. This is basic BEFORE you start to hassle the computer. Jerry