I have a 1995 Chevrolet C1500 5.7L, 2wd, automatictruck that has an intermittent SERVICE ENGINE LIGHTthat comes on when the truck is in PARK. It goesoff when you increase the RPM's. Truckis idelingbetween 900 -1000 RPM's in PARK. Have not ever seen light come on when in DRIVE. When stopped at a light with truck in DRIVE, the RPM range is between 700-800 RPM's.

Been to AutoZone and was told the code indicated the Air Intake Control sensor (IAC)needed to be replaced. To date I have replaced it twice, and still have thesame problem. Replaced the Throttle Position Sensor (TPS) also. All electrical connections appear to clean and good. No apparent vacuum leaks.

Need to resolve to get inspected.

Thanks!

 

If it is a TBI, check for vacuum at the PCV valve. If there is none, buy a throttle body gasket and take the throttle body off and clean all the carbon out of it

 

Thanks for the great advice. The truck does have a TBI and A/C. I replaced the EGR valve about a year ago, but will test it. I have sprayed the TBI with cleaner, and there are no misfire codes to date.

 

Thanks for the suggestion. There is good vaccum from the PVC valve. I have had the thought to remove the TBI and break it down to clean. Have not looked into securing a gasket set.

 

When you replaced the TPS did you check and adjust the voltage output at idle and WOT ?