?? Idel Air Control Valve?? [Archive] - GrandAmGT.com Forum


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Bill P.
05-04-2006, 06:06 PM
Have a 2.4 1997 GA that is driving me crazy.

Idleing rough, (surging, may be too rich). Runs great on the highway.

No vaccum leaks.
Code reader showing P0300 (misc. cylinder miss, of course I could tell that).

New Plugs, New plug insulators.

Has a very small air leak in the throttel body to intake manifold. (changed vaccum reading about 1.5 lbs with the new gasket). I have replaces a couple of short hoses and did a spray check for other leaks in the manifold/throttel body area with no additional leaks found.

I have had most of the other components except for the EGR valve and the IAC checked and they are good.

I am only guessing but would the IAC valve cause it to run rough??

When I pull the full vaccum hose off the throttle body to check the vaccum it actualy smothes out a little, that is why I think it is running rich at idle.

I am ready to give up and throw $$ at a shop for the 4th time in the past 15 years.. Kind of hurts my pride..:confused:

05-04-2006, 11:34 PM
The IAC ensures you have enough air for the engine to run decently at closed throttle. According to what you've said though its out of the picture. Dumb question but how did you test it?

A rich condition could be something else entirely. Basically its common to all cylinders and only at idle right? My first thoughts are MAF and/or o2 but then you'd see problems across the rpm range.

Bill P.
05-05-2006, 06:32 AM
Had a friend at a shop test the IAC. That may not be 100% but he has come through before for me. The only reason this old shade tree mechanic thinks it could be the IAC is that it runs smoother when I pull a vaccum connection off the throttel body -the full vaccum connection below the throttel plate- it runs better with the port open, more air coming in.

Bill P.
05-05-2006, 06:47 AM
The first check I ran with my code reader showed a bad front 02 sensor and the P0300 code. The 02 sensor was the first thing I put on this DOG and the code has not returned. I am working from a Haynes Manual, limited information in the area of my problem.

I have NOT CHECKED the MAF sensor. Is there a way to check it with a VOM meter?
I did a visual and it is not crudded up. It has not set a trouble code either.

It has set some trouble codes that were in error. My friend said a vaccum leak could cause this. I beleive I have found and repaired the only small vaccum leak-gasket, throttel body to intake manifold. I have sprayed WD40 around the other areas where there could be a leak and did not notice any difference in the idel speed.

The only code that keeps repeating is P0300. Random misfires.

All suggestions are welcome.