Chevrolet Repair: 4.3 l chevy s10, vacuum leak, eiac

Question
i replaced every sensor i can think of, cut off the catalytic conver to let it breathe because of possible clog and replaced fuel filter, also did tune up. my question is why will this truck not idle? cannot adjust idle its a 90 so its computer controlled. does temperature sensor control automatic choke because temp is not registering on dash. thanks

Answer
Hi Andrew,

 The temp sensor for the cluster and for the computer are different sensors.  The computer actuates the IAC valve to determine what idle speed the engine needs to be at based on the ECM's target idle.  This is done by controlling a metered vacuum leak.  The IAC valve is basically a servo that controls a vacuum leak around the throttle plate. If you introduce a small vacuum leak and the idle goes up and doesnt come down means that th eIAC is not in control of the idle.  It could be the IAC, the computer ro wiring.  If would like to know more info on IAC operation email me back.

Wayne