The IAC valve lets air in behind the throttle plate and thus has nothing to do with the throttle opening. The throttle plate is spring-loaded to close but not completely. I thought there was a screw to adjust this minimum throttle opening.

 

Idle speed solenoid. No adjustment screw, all measurements set by the PCM. Under load with AC on the idle is even? Possible vacuum leak on the intake? Or spark delivery issue, distributor, cap or wires. Check for vacuum leak.

 

Well I got some good news. I took everything off all the way down to the intake. Installed new intake manifold seals and followed some online directions on how to bolt down the intake. Now she purr's like a kitten. Also put new air filter and fuel filter on her. Thank you all for the suggestions!

 

great, so it was a vacuum leak then.

 

You may check that the serpentine belt adjustment is correct, when the AC is on there is a considerable load placed on the belt, and if it is out of adjustment and normally running loose the computer and sensors may not be getting the proper voltage supply due to the alternator slipping on the belt, but the problem will be fixed by the extra tension on the belt with the AC on.
The gorund strap on the right head should run to the frame rail just under the heater core hoses, as should the ground from the firewall. Any good engine ground can work such as the manifold, but this defeats the purpose of the wire in the case the others fail.

 

Could be running to lean for some reason. Mine did the same and it was an O2 sensor. It started losing power and at stop lights it would idle at about 600 and shake the truck. Took a month for the sensor to throw the code but it fixed it when I put a new one in. It's done the same thing twice now

 

I'm just pasting my same responce here that I put on a much older post. I think the last thing we check with this issue is the toughest to replace. Yet the most common "well duh" repair to check. Here goes.

Same deal on my 94 k1500. Just bought it a week ago. 4k miles on rebuild. Engine tranny transfer case redone. Everything but the little things. Ran like a champ for a week then it started surging untill it stalled out on idle, especially if lights+turnsignals on. Unplugged IAC ran good for a day then back to the issue. Changed that out, it ran about 20 miles fine then, back to the same idle behavior. Noticed the rattle in the catalytic, changed it to magnaflow. Felt better driving, when in idle, same problem. Checked fuel pressure and it found to be low. Changing out fuel pump today. I'll update you after its installed.. In the end hopefully having all the little things updated also will keep this beautifull heap going another 200k miles.

 

Please advise if this fixes the problem ! I've got the same thing going on with my 1995. No problems up until last Saturday. Sitting at a red light and it started idling rough, it went away. Then on my way to work a few days later got really bad now it lopes and surges at idle all the time.... tried O2 sensor, fuel cleaner and replaced the fuel filter no help. Shop manual suggests vacuum leak but I cant seem to locate................

Ray

 

When I built my engine, it had a vacuum leak. I didnt mount the intake properly, spraying starting fluid around the intake is how I found it. Right when I got near the EGR the engine would die. So after some research and a new set of intake gaskets, I got her mounted properly, with no vacuum leaks. I also retimed my motor, she runs much better but still surges at red lights, she doesnt die though. I want to replace the fuel pump, but dont really have the time to do it. Im sure its prolly the original in there. A buddy of mine asked me if it died while driving down the road or highway, answered him NO. He said dont worry bout it then! With a big smile.

 

Sorry for not reposting aftewards. In any case. It was the FUEL PUMP the whole time. After driving about 5 miles it has been running like Forest Gump. Just do it man, atleast check the fuel pressure. I swear its the simple things.