Hey guys,

Just picked up a 96' t100 4x4 MT from a close friend of mine as a new project. Truck has 233,000 miles on it and the valve gaskets are leaking so im getting ready to change them out. However the truck is idling really high (anywhere from 1100-1500 rpm) When i start the truck up it idles really low (around 500 rpm) but then builds up. I need to get it down to get the truck to pass smog and i know its not running right. I have done some research and found that it could be the IAC? Any suggestions you guys have would be great. I'm avoiding going to shop as its not my daily driver and i'd like to work on it myself. '

Thanks

 

A bad TPS will cause the exact symptoms described.

The ECM opens the IAC once the throttle has opened to a certain point. If the TPS has a glitch (which could occur only when the TPS is warm), the ECM is mislead into thinking the throttle is open when it is actually closed; therefore the IAC remains retracted when it should be closing to regulate idle speed.