I have a 1991 s15 Jimmy 4.3L carburated truck and my truck failed air care with high idle hydrocarbons. I am looking for the screws on the carburator to adjust the idle/fuel mixture. Anyone able to tell me where these are, I can't seem to find them.

 

A 91 didnt have a carb from the factory it was throttle body injected. You most likely have a sensor going out and not bad enough to throw a fault code.