Project 3.4 Camaro

Engine can't hold a steady idle with the IAC connector plugged in, but when I unplug it, it idles perfectly fine....I believe its bad...

Project 3.4 Camaro

and also is it driveable with it unplugged, as long as idle is ok? Or would that cause other issues?

Maverick H1L

iTrader: (8)

Which top end are you using? If it's the old 2.8 top, check for an air leak in the piping to the rear of the intake.

And yes, it's driveable. I didn't have a working one for about 2 years after the 3.1 was dropped in. Only thing is that you will need to adjust the minimum air to net you about 900 RPM cold and that the idle speed will INCREASE as the engine warms up instead of dropping.

Project 3.4 Camaro

its the 2.8 one, and air leak at what pipe on which manifold? and I meant driveable with IAC unplugged in case that wasn't clear..

Maverick H1L

iTrader: (8)

If you're running the 2.8 parts, there should be a large nylon pipe that connects the IAC passage in the TB to the inlet nipple on the intake manifold. With the weather up here and the age of the pipe, it could have come apart or broken somewhere. Also check the boots on the end of the pipe for cracking. These can be replaced with short lengths of coolant hose. Believe it or not, GM seemed to have a brain fart when they designed our engines and that pipe is how the IAC controls the air flow into the intake, not a passage into the plenum like on the later 90-92 cars and the GenII +. Without that pipe, the IAC is actually creating an air leak into the bellows behind the MAF, which is a bad thing.

And yes, I know you were referring to running without the IAC connected. Like I said above, I ran without one for almost 3 years. Because I didn't have a working one and I didn't have the pipe. The passage was plugged right off to prevent a post-MAF air leak.

Project 3.4 Camaro

oh you meant the IAC vac hose, yeah its fine, I was actually going to altogether replace it at one point but could not find any plastic ones and suspected what I had was collapsing under vacuum, so I put some hose on the ends, I have some rubber vacuum caps on things, namely the rear of the plenum and the one end of the , they are pretty cracked, any chance thats causing some of my issues?

Maverick H1L

iTrader: (8)

When I went to the dealer to find a replacement idle air bypass pipe (IIRC as the dealer called it), it was listed as NPN (no part number) and not serviceable. You can, however, get some coolant hose and a couple 1/2" PVC fittings and make your own. And yes, if the rubber port caps are cracked, they're probably causing air leaks. Any leak after the MAF is bad, as you probably know.

Project 3.4 Camaro

Heh...you should've heard it when the intake manifold wasn't sealed well....if dogs had nightmares, they would be about a hellish vacuum cleaner that would sound just like this noise it was making...and it was loud, REALLY loud...

Maverick H1L

iTrader: (8)

Yep... Not long after I got the 2.8 stuff working, my upper plenum decided to crack and break right at the upper TB mounting ear... That whistle was SOOO loud it wasn't funny. Cost me $40 to have that fixed, and the shop that welded the ear back on screwed it up and I was forced to use a gasket and a half to seal the TB right (uneven on the driver's side even though I told the guy that the TB mounting surface HAD to be PERFECTLY FLAT). Which is why I finally replaced it with 3.1 parts. And then the crappy air intake I bought did pretty much the same thing because it's such a pain trying to fit our IAT into one of those that doesn't have the bung.

I can't wait to find out what mine finally sounds like WITHOUT an exhaust leak as well. If one engine didn't have leaking parts, the other did.

Project 3.4 Camaro

btw how do i get that stupid metal cap that looks like a freeze plug out of the throttle body to adjust idle speed? If I have to run without the IAC connected I need to lower the RPM so i dont peel out just by putting it in gear...

DeathStarr89

iTrader: (1)

just grab one from the junk yard.. lol


Have you taken it out and cleaned it? Done an idle re-learn?

FireInMe17

Probably the best place to start, you can clean these things and prolong the life of the sensor for quite a while. I used to just pull mine and clean it every few weeks or so to keep it working the way it should. You'd be surprised how quickly they get all gunked up being such a small part.

Also, clean the part of the throttle body that it plugs into, if you clean the IACV and don't clean the passage you might as well not even clean the valve in the first place.