1990 truck won't idel when cold

I have a friend that has a 1990 Chevy truck with a 4.3L. Lately he has been having problems with it. When he first starts it up it will not idel when it is cold. If he revs the engine and keeps his RPMs up the truck will run, after it warms up it idels just fine.

He has changed his EGR valve, his PCV valve and a few other things.

Does anyone have any ideas?

bad iac motor. easy fix

bad iac motor. easy fix


What is a iac motor, please define.

sorry, idle air control motor... screws in the front of the throttle body on that engine, has, i believe a four pin square connector and if im not mistaken comes out of the throttle body at about a 90 degree angle.

sorry, idle air control motor... screws in the front of the throttle body on that engine, has, i believe a four pin square connector and if im not mistaken comes out of the throttle body at about a 90 degree angle.


Is this the Idle air control motor or valve?

BEFORE YOU REPLACE THE IAC, MAKE SURE THAT THE LITTLE BUTTERFLY VALVE IN THE AIR INTAKE IS CLOSING WHEN THE ENGINE IS COLD, THIS COULD ALSO BE CASUING THE CONDITION YOU MENTION. i WOULD THINK IF THE IAC WAS BAD, THE IDLE WOULD BE BAD HOT OR COLD. I BELEIVE THIS VALVE IS VACUUM CONTROLLED ON OYUR TRUCK, SO IT COULD JUST BE DISCONNECTED OR LEAKING. hOPE THIS HELPS

Could also be a bad coolant temperture sensor.

Could also be a bad coolant temperture sensor.

That is exactly what I was thinking. If you disconnect it and the truck idles cold, then the sensor is bad.

By disconnecting it, the PCM will think the engine is real cold.

//2000CAYukon