IAC valve

[daves87rs]

OK, now it's warm enough to get to work on this thing.

Tell me as much as possible about the idle air control valve.

I'm pretty darn sure this what it is, though it's tough to get a reading on it, because a few times it tells me different parts.....

I'm replacing the IAC, fuel filter, PCV.......

I'm hoping this will stop the rough idle (much worse in warm weather/warming up a while), SUV gas milage (it's back), and the lack of pick-up that it has...and the fact that changing speeds (mostly slowing down) throws the check engine light on....

If this doesn't work, I'm going to assume it might be something worse....

[76ChevyTrucker]

All right, the Idle Air Control Valve, or IAC, acts similar to the choke on a carbureted vehicle. At idle, it allows air to bypass the throttle plate so that idle can be maintained. It also helps when the engine is idling and high-load devices (A/C, alternator actually charging, etc) are running by bumping up the idle just a tick so that they won't drag the engine offline. Normally the EGR valve will empty out ahead of the IAC, which allows the same little chunks of carbon that can stick an EGR valve up to clog up the passage way that the IAC sits on top of also. As good advice, if you do replace the IAC, invest in a can of carburetor cleaner and spray out the passageway that the IAC is mounted to as best as you can before putting a new IAC back in there. That way you not only have a new IAC to do its job, but you'll also have a good, clean passageway for air to flow through.

Another thing, if you take the PCV valve out of its valve cover and shake it and still hear the little valve in there rattling, then its all right, you won't need to replace it.

[daves87rs]

All right, the Idle Air Control Valve, or IAC, acts similar to the choke on a carbureted vehicle. At idle, it allows air to bypass the throttle plate so that idle can be maintained. It also helps when the engine is idling and high-load devices (A/C, alternator actually charging, etc) are running by bumping up the idle just a tick so that they won't drag the engine offline. Normally the EGR valve will empty out ahead of the IAC, which allows the same little chunks of carbon that can stick an EGR valve up to clog up the passage way that the IAC sits on top of also. As good advice, if you do replace the IAC, invest in a can of carburetor cleaner and spray out the passageway that the IAC is mounted to as best as you can before putting a new IAC back in there. That way you not only have a new IAC to do its job, but you'll also have a good, clean passageway for air to flow through.

Another thing, if you take the PCV valve out of its valve cover and shake it and still hear the little valve in there rattling, then its all right, you won't need to replace it.

Sweet...

Question though-What if it fuel injected-not carbureted?

I heard it's also a common issue on the 3.1s..(like mine) Is that actually true? (not sure on this one)

[76ChevyTrucker]

Well, the IAC valve actually more or less replaces the choke from a carbureted vehicle on all fuel infected cars and trucks. The 3.1, as far as I've heard, doesn't eat IAC valves, really its the Ford Mod engines that do that a lot, and EGR valves. But it shouldn't be hard to change, look around on your throttle body, and it should either be the screw in type and you just have to get a wrench on it and twist it out of there, or it'll be the plate type with two bolts holding it in place.

[daves87rs]

Well, the IAC valve actually more or less replaces the choke from a carbureted vehicle on all fuel infected cars and trucks. The 3.1, as far as I've heard, doesn't eat IAC valves, really its the Ford Mod engines that do that a lot, and EGR valves. But it shouldn't be hard to change, look around on your throttle body, and it should either be the screw in type and you just have to get a wrench on it and twist it out of there, or it'll be the plate type with two bolts holding it in place.

Hmm...in early 90s Cavaliers(93)- the IAC would be on top of the engine-toward the back-right?

(Think I've spotted this little guy before)

[Buickfosure]

What engine is in it since I had the 2.0L in my 93 sunbird before I sold it. It had a rough idle and I replaced all the obvious but never the IAC valve. Just curious since I was never able to diagnose the problem, but I never had a check engine soon light come on.

[daves87rs]

What engine is in it since I had the 2.0L in my 93 sunbird before I sold it. It had a rough idle and I replaced all the obvious but never the IAC valve. Just curious since I was never able to diagnose the problem, but I never had a check engine soon light come on.

A 3.1 in my 93....

I've replaced a bit already, but to no success....

My check engine light will come on and off...almost seems confused at times....

[76ChevyTrucker]

And it could be. The OBD-I computer system on your car could only see problems that directly interfered with vehicle performance. It was unable to evaluate the performance of different parts (OBD-II can). So in fact, it could be confused. For a shot of the part, go here :https://www.mycarquesthomepage.com:8443/acl/?mfgName=CARQUEST/STANDARD MOTOR PRODUCTS&partNumber=AC5 That should give you a good picture of the part.