I am having a weird idle issue.

Car starts and runs fine, but when driving and engine gets to 1500 RPM, it fluctuates wildly to 2500 RPM and back to 1500 without any input from me.

I have tested, repaired, and replaced just about every component.

Code 55 (cool but I would rather have a code that I can use to diagnose with).Injector terminals were corroded - fixed that - much better.Ignition Coils are good.TPS is good.CPS is good.PTU is good.ECU is good.

I am pretty much narrowed down to Idle Valve/Control.

I bought a used valve on ebay from Ultimate Z and wanted to test it before installation. I was told that a good test to be sure these things are working is to put power to one terminal and ground to the other, and it does not matter which goes to which. When powered, the valve should close. This one does not close.

Is this test accurate?

Does anyone have any other ideas about what may be wrong?

If I were to guess - I'd say it's a problem with your MAF. I'd think the AAC valve is too slow to react to cause such a quick fluctuation...

I had a MAF issue on my Q45 and the symptoms were very similar to what you describe.

Heath

That is very interesting....and a very distinct possibility. We replaced the MAF a while back, and I am pretty certian that the idle issues followed soon thereafter. We did not notice the possible connection because this car has had so many weird issues that I overlooked it.

Will try to swap the old MAF in tomorrow and see what happens.

Will get back.

Well, I am back to square 1. Swapped out the MAF and the IACV - nothing.

Tell me if this logic makes sense:

1.) When stopped and in neutral, when you rev the motor, it grabs at about 1500, races to about 2100, and back down again over and over.

2.) When moving in first gear, it grabs at about 1500, races to 2500, and back down again over and over.

3.) In second gear, it grabs at about 1700, races to 2100, and back down again, etc.

The point being that this seems to be more of a vacuum related item than a mechanical one becase the RPMS change their start and stop point depending on speed, gear, load, etc.

That said: EGR Valve?

HELP?

i had this problem as well and it turned out to be my hard pipes on the intake was out a little bit causeing to much air to get in through the throttle bodies, i just put the tube back in and it is fine now. make sure you check a** air lines and vacume hoses this could take part in this problem, once in a while when it is cold out and the car sat for a while it will do it still but rairly.

Hard Pipes? What are hard pipes? Too much air to the throttle bodies? I am very confused - lol

He's just saying check for any vacuum leaks, as that could be a cause. Also, you have checked your ignition timing right? You can use a timing light to make sure your spark plugs ignite at the right time. I learned for myself that if it isn't at 15 degrees before top dead center, it can run horrible at certain rpms.