sstang

I have done the IAC mod and the car still runs the exact same. It hangs at 1500 rpms, and idles at 1000-1100 rpm. The car runs perfect with the IAC unplugged, but I get a CEL so I'm trying to come up with a fix.

What would happen if I put a solid gasket for the IAC where nothing would pass through?

cliffyk

If you block the IAC the car will run like crap, and probably not idle at all.

It sounds to me as though the IAC is fubar. Have you tested its resistance, should be 6 to 13 ohms;

If not, buy a new one...

If it is then:

Disconnect IAC valve.
Key on, engine off.
Measure VPWR circuit voltage at the IAC valve harness connector.

Is voltage greater than 10.5 volts?

If so then buy a new IAC because the one you have is jammed. You can try cleaning it, however this is what the shop manual says about the IAC:

If not you have an electrical/PCM problem...

sstang

Cliffyk, I will try seeing what kind of numbers it is putting out. However, I think it is unlikely that the valve is bad b/c the car ran fine, I swapped on a new TB/plenum within an hour, and then this problem started.

And you say the car would run like crap with it blocked off? Idk if it would b/c right now it is completely unplugged so it is not working at all, so it's basically just a vacuum line right now being used for nothing. I mean it's worth a shot since it only takes 5 minutes, but I also doubt that would fix it. I will get some numbers tomorrow and let you know. Thanks for the help.

cliffyk

I believe the valve defaults to "open", I.e. the signal from the PCM pulls it closed.

In any event however having it unplugged could/would cause the symptoms you describe as the PCM will have no control over the idle speed at all.

sstang

Well cliffyk I got some readings from it today and everything is in spec. I tried using a solid gasket to block it off..... and IT WORKS! The car idles, revs, and runs normal like that, and this way I can leave the sensor plugged in, so no more CEL either. I've never heard of anyone else having this sort of problem, but this works for me. I live in NC and there isn't really any cold weather often so I guess I'll be fine like this.

Thanks for your help though.

I'm thinking since my plenum is blocked off now I may try blocking off the intake pipe hole as well and see how it does.

cliffyk

You have a vacuum leak, the TB is misadjusted, or the TB is leaking air when it's "closed".

What happens if you turn on the AC?

[edit]
A bad PCV valve (stuck open), or leaking PCV hose could cause this. Are you sure you reconnected the PCV hose securely, at the back of the plenum?

sstang

The TB closes fine, and adjustment I know is fine. If anything it's a vacuum leak (which I think it is), but it is VERY small. There is no noticing any roughness in the idle. I tried using a squirt bottle with soap but with no luck. Are there any other tricks?

And I noticed a little oil around my passenger PCV so I'm going to pick up a new PCV valve when I go to work. Good suggestion, perhaps it's there. I know the back of the plenum is plugged in good.

With the AC on, the idle drops from about 850 to 650. There's no cutting off or anything happening though. This is just a temporary fix though, b/c I do want the IAC working.

cisurfer

i have the exact same problem i have a 75mm tb and plenum but its been on the car for awhile and out of no where it started doing this idk what to do i replaced the iac and it still does it