2003 Ford Taurus - Idle relearn issues

[mmk]

About a week ago, my Taurus decided to turn its engine off on a city road. After turning it back on, I noticed that the engine was revving up and down a lot. This happened one other time and I took it into a shop.

They ran diagnostics on it and said that they got the computer to throw an Idle Air Control code, and suggested I replace the IAC valve. Since then, the ECM is having issues relearning the idle. The mechanics reset it multiple times but it won't fix it.

As soon as I turn the engine on, the RPM revs up a little over 3,000 for a few seconds, and then comes back down to around 600-800.
When I put the car in drive without the AC on, the RPM stays around the same place until it gets gas. As soon as the car gets gas, the RPM stays well above 1200, and in fact starts accelerating slowly on its own. If I go long enough, it even moves on to the 2nd gear. If I try to come to a complete stop, it is pretty hard to do as I have to ram the brakes all the way. At this point, the RPM drops down to about 1200 and I can feel that the car is trying very hard to push against the brakes - it starts vibrating and I can feel the pressure against the brakes. If I keep my foot on the brake long enough, it eventually drops back down to 800 and keeps moving around between 600-800 until it I hit the gas again.

If the AC is on and the car is in park/neutral, the engine keeps revving between 200 and 1500 and does not stop doing that. When it's around 200, the battery and the oil lights come on momentarily before it revs back up.
On the driving gear, it does not act very differently, aside from the fact that the idle is a little bit lower (1100 ish) but still higher than it should be.


The mechanics seem to think that the car has a bad ECM and want to try replacing it. I personally think that though it's kind of a pain, the issue is somewhat manageable. I realize that this is going to put a lot of stress on the brakes, but is there any other wear and tear or anything that may go wrong because of this idle issue?

Further, what's your take on this? Does it sound like the ECM needs replacement or could it be a simpler fix?


Sidenote: The car has had an Insufficient EGR flow code for a month now. However, the code showed up even though the car has a new EGR valve, solenoid and tube. The mechanics think that this is another sign that the ECM is faulty, because it's throwing codes for no reason. Granted, one of the replacement parts could have been bad but what's your take on that?

I appreciate all the help I can get!

[shorod]

Everything you're describing sounds to me like you have a vacuum leak somewhere, which can explain everything you describe from the original fluctuating idle (even before the IAC was replaced) as well as the EGR flow codes.

FWIW, if the shop you visited has not yet suggested that there might be a vacuum leak and instead are suggesting the ECM is throwing codes for parts that don't seem bad, I question their understanding of anything other than reading diagnostic codes. Diagnostic codes are not intended to state which parts are bad, but rather which systems need further diagnosis.

-Rod