97 k 1500 5.7 vortec

[Rojo]

I have a 97 vortec 5.7.
It idles high when I put it in gear drive or reverse put it in park or neutral it idles normal.
What would cause this. I have not done anything to it other than alternator and idler pulley

 

[Schurkey]

Connect a scan tool, verify ALL the sensors and computer outputs, especially the IAC.

Verify commanded idle speed vs. actual idle speed.

 

[Orpedcrow]

Probably the IACV, but like schurkey said, you’re going to need to hook up a scan tool to really know.