97 SLP Company Car

Ive been getting a random misfire mainly just at idle and in the process of checking everything,ref voltage to all sensors and res on the ones I could reach I couldnt get the probes on the iac to check res. So later on after the car was in closed loop I figured I would just unplug it and see what would happen. No change in idle at all revved the hell out of it and idle would still come back to 1050 every time along with the shaky idle and no ses. Just to make sure computor was working I dissconnected tps and idle shot way up and kicked a ses instantly. Somebody please tell me this is proof the iac is shot and not to keep looking at opti.

Injuneer

If you pull the IAC motor connector off, the pintle will stay right where it is at, so the idle will stay right where it's at. The idle staying the same wouldn't prove anything.

If you suspect the IAC motor is contributing to a rough idle somehow, you need to get a scanner on it, and see how the PCM "counts" for the IAC are moving, and whether the engine idle speed is responding as indicated. Look at the counts at idle. Turn on the A/C... the IAC counts should increase slightly to compensate for the added load from the A/C. The idle should hold constant, even though the IAC counts went up.

Why do you have a 1050rpm idle? Is that where pcmforless set it?

97 SLP Company Car

Thanks for the reply. I never questioned the idle speed because Ive owned the car almost five years and the idle speed has always been about 1ooo rpm even before hot cam. It never seemed that high to me with an m6.Mechanic at matick chevy here in mich that does diag told me exactly what you said about position unplugged and such.The only thing he did say that about the iac is it should have some movement and without crushing it I cant budge the pintle at all.I dont have a scanner but I didnt have any codes a week ago and still no ses just random misfires mainly at idle.Today front of motor is coming off (opti) and new wires, water pump and hopefully just cap and rotor on opti.At 90000 miles this is typical I guess. Thanks fred.

shoebox

An IAC that has been in service is extremely hard to move without damaging it. So much so, that the factory manual says NOT to try moving the pintle. A new one can be moved when installed, to match the position of the pintle on the old one.

97 SLP Company Car

Thanks alot guys I know you two are probably the most knowledgable on the site and I probably did damage it when I cleaned it, bought a new one yesterday at dealer.

Right now all I have left to get off front of motor is balancer but so far I did find something, coolant temp sender in water pump, one of the wires to it is missing a piece of insulation and wire is all corroded.Seeing that the comp is looking for return voltage from that sensor I know any res will give a false return signal. I will get this thing perfect even if takes two to three days to get it back together.Your help is invaluble,thanks again.