IAC Idle Air Control valve replacement in 1992 C4 Corvette

A video documenting my experience replacing the Idle Air Control valve in a C4 1992 Chevrolet Corvette. The replacement was done to fix a problem of hard-starting when warm combined with very low idle RPM when cold. With the right tools, I was able to do the job without removing the throttle body :-)

[@ObscureStuff420]

Thank you, this is very detailed and helpful. I just bought a 95 that looks just like yours, same color. Idle is a bit rough and it wants to shut off sometimes so I'm going to give this a shot and see if I can get away with just cleaning it and making a gasket. Wish I had known about hose clamp pliers years ago, those things have caused me to utter quite a few curse words.

[@MegawattKS]

Cool. Hope it helps ! I think my '92 and also the '95 fell just short of having the OBD2 connector to read codes with normal readers. I had an '88 Chevy long ago that helped me diagnose a fault in the MAF sensor using the paperclip method - but I don't think the Corvette has the MAF. Will keep my fingers crossed that your idle improves ! :-)

[@ObscureStuff420]

@MegawattKS the 95 is weird. It has an OBD2 type connector but is still only OBD1. It does have a MAF, I think they added them starting with 1994.

[@MegawattKS]

@@ObscureStuff420 Interesting. Even on the '92, I am able to get some information out using the connector. I built a special wiring harness to short some pins together without having to bring out my trusty paperclip. I can read some stuff (and even control things like locks) through the instrument panel and the gauge buttons. Corvette was definitely ahead of their time ! 🙂

[@ObscureStuff420]

@MegawattKS I've got an 89 Celica I've had abt 22 years. Not driving anymore due to a massive oil leak from a ring worn under the camshaft seal, but several years ago the CEL came on for the one and only time it ever did. I had to stick a paper clip in a plastic terminal under the hood and count the flashes of the CEL to determine the code, which was caused because I knocked a sensor loose.

[@Chloe..3]

Very thorough, thank you

[@MegawattKS]

Glad it was helpful!

[@lindyp38]

Thanks. I recently did mine.

[@MegawattKS]

Excellent. Great cars !

[@antoniosapoenza-hd2sp]

you had to adjust the valve pencil again without breaking it because I changed the sensor but the engine was running at 1500 rpm with the explanations in the factory manual

[@MegawattKS]

Interesting. What model-year? My '92 has a self-calibrating adjustment of pintle done by the ECM. It worked perfectly after the auto-calibration finished (that is, after I actually did the right dance to tell the computer to calibrate it).

[@antoniosapoenza-hd2sp]

mine is a 1992 model and I have followed the procedure in the FSM manual but I am unable to adjust the engine idle, if instead I turn on the ignition without turning on the engine and lower the throttle all the way and then turn on the engine without accelerating for 5 seconds, then I turn it off and on after 10 seconds is it the same? Now I no longer know how to reset the IAC valve to bring it back to its original state

[@MegawattKS]

@@antoniosapoenza-hd2sp Hmm... I'm re-reading the FSM instructions now and trying to envision what sequence of actions is required to let the computer know that it is supposed to run the cal. From what I'm reading, here's my interpretation: With car off (they don't say that), press accelerator slightly. Then start the engine, and after its running, release the accelerator - and let it continue to run for 5 seconds. Then turn it off for 10 seconds, and then restart. Is that what you did? It sounds like you may have released the pedal before actually getting to the run position first. (Here's what the FSM says. It's kinda vague, and the above is just my interpretation of what this says: A. Depress accelerator pedal slightly. B. Start and release accelerator pedal, run engine for 5 seconds. C. Turn ignition OFF for ten seconds. D. Restart engine and check for proper idle operation.)

[@antoniosapoenza-hd2sp]

thanks for your reply I'm only replying now because I ordered a new iac valve to do the procedure again but you say, pressing the pedal with the key on or off maybe this is what I'm doing wrong?