I have a 1992 S10 blazer 4.3 W engine that no longer idles up at start when cold. What determines or sets idle? I changed the ECM but it didn't help. Also cleaned idle air control valve.

 

Hmm. Check the coolant temp sensor. The one on the front of the manifold. It tells the ecm the temp of the engine. If its cold its suppose to tell the ecm so it triggers the iac to idle it up. Try it this way,unplug it,start the blazer cold. then plug it in and start it. did the idle change at all? if not id replace it. they are only like 13 bucks.

 

Thanks for replying Chris. I replaced the temp sensor about a year ago. I'm leaning away from that because I can feel the vehicle go into closed loop mode after I drive about 1/2 mile...depending on how cold it is outside. I have an old one that is still good that I could put back in. I'm thinking this is something that seldom goes bad, but what about the prom chip?