2000 chevy silverado 1500 4.8 idles at 750 in park but when put in reverse it goes up to about 1100 and back down when in reverse to 600 same thing happens when going to nutrail and drive and same happens when going back to park. it trips a po507 code higher than expected idle

 

1) Remove the air intake from the throttle body and inspect the air bypass port/valve for excessive carbon buildup. Clean as needed.

2) Have a helper turn the key on, then off as you observe the IAC through the bypass port. At key off, the pintle should extend all the way out to close the port, then retract a little. If this doesn’t happen, or if the movement is “choppy” or noisy, replace the IAC.

3) There was a service bulletin from GM that an updated PCM calibration could fix this type of surging. It didn’t specify any codes but may be worth looking into.

Try looking under the hood for a sticker (could be on the under side of the hood, next to the emission label, on the fan shroud, or on the throttle body) that notes a calibration was performed. If you don’t see one, call your local dealer with the VIN and ask them if it’s been done. If not, they can estimate the cost of the service for you.

 

ok thanks! ive taken apart and cleaned everything so looks like checking in with the dealer.