2000 Taurus Idle Problem

[jayzenner]

I have a 2000 Taurus wagon (3.8L engine) that, until now has been the best car I've ever owned, and I've owned a lot. I've put almost 116,000 on it since I bought it new and I had NO problems with it during the first 85,000 miles or so. But now I'm having a problem that my mechanic can't seem to solve. Basically it is idling erratically and I have the check engine light (code PO1056) on most of the time. Most of the time the idle seems high and occasionally it will rev up to 1500-1600 rpms for a couple of seconds and then slowly decrease to around 1100. This is pretty predictable if I put the car in park without shutting it off but it happens other times too when I just let off the throttle in drive. This happened once pulling into my driveway and I would have parked in my living room if I hadn't hit the brakes hard. It will also do it if I give it a little gas in park and then take my foot off the peddle.
The first attempt at a fix was replacing the idle air valve as the code indicated. When that didn't work, the assumption was that we'd gotten a bad one and replaced it twice more. The mechanic then checked for a vacuum leak and determined that I had a warped intake manifold. So that was replaced with all the gaskets and the upper radiator hose and there doesn't appear to be a vacuum leak anymore. They road tested the car putting about 20 miles on it and the check engine light stayed off but the idle still wasn't right. I wasn't 200 yards away from the shop before it came on again when I drove it home. The mechanic thought he might have damaged an air sensor with cleaner so he replaced that. Still had the idle problem and after a day of driving the check engine light came on again. Now he wants to take the car to the Ford dealer to get a flash memory update to the computer and says if that doesn't work, I'm looking at an expensive new computer for the car.
I searched the other threads and saw a couple of similar problems but no definitive fixes. What really concerns me is that I didn't see any mention of the computer possibly causing the problem and I sure don't want to spend a grand on this if it's not related to the problem.
Any suggestions? There have always been good vibes between me and this car but I'm losing confidence in it as fast as I'm losing confidence in the economy. Thanks.

[LastTudor]

You do not have a 2000 Taurus with a 3.8. The last year of the 3.8 Taurus was 1995. I'm sure you meant 3.0 and it was just a typo. Anyway,

The idle problem is interesting. I'm not convinced that all the vacuum leaks are gone. If they think the computer is the problem, then they must think that the signals to the computer, especially the crank signal, are all fine. They must think that the signals from the computer, especially the signal to the IAC are all fine. Frankly, if they just want to throw a computer at it, they're not using their shop manual and testing the components they should.

I'd be more apt to believe that there's an undiagnosed vacuum leak.

[jayzenner]

Of course you are right about what engine is in my Taurus. I picked up the 3.8L from one of the service orders which I'm sure was a typo. The engine is the 3.0L DOHC Duratec engine.

So, you think I should ask the mechanic to check the crank signal to the computer and the signal from the computer to the IAC and to check again for vacuum leaks?

If I understand you correctly, updating the computer's flash memory or replacing the computer would not solve the problem if it was getting an incorrect crank signal. Am I correct in assuming that a well equipped garage would have the equipment to test this? What does a bad crank signal imply? Is that a major problem?

I forgot to mention yesterday that when I took the car after the other repairs whether there was any problem starting. I told them that starting cold it stumbled a little bit until I put it in gear.

I trust my mechanic to do the right thing and I know he's puzzled by this problem but I am not a mechanic and have no basis for judging whether he really knows what he's doing, so I really appreciate your "second opinion." He has been talking to some sort of hot line Ford apparently maintains but I don't know whether to trust it or not. I already have about $1300 invested in trying to fix this but I'm not sure how much sense it makes to keep pouring money into it. Thanks.

[LastTudor]

Originally Posted by jayzenner

If I understand you correctly, updating the computer's flash memory or replacing the computer would not solve the problem if it was getting an incorrect crank signal. Am I correct in assuming that a well equipped garage would have the equipment to test this?

A Ford dealer would have been required by Ford to buy all the tools and manuals applicable to your car. A non-Ford repair shop may not have the right tools or manuals.

Even if they have them though, they may not use them as they should. Diagnosis is not always fun to the tech, especially when they find frustration like your car has provided. But with modern test equipment and test procedures there are pinpoint tests that should be followed to find the specific problem your car has.

I think you need to lean on them to prove that what they're replacing is actually the problem. There's no reason for a Dealer to throw parts at a car.

[theoldwizard]

First, "PO1056" is not a legal error code, so it is not of much help.

Originally Posted by jayzenner

So, you think I should ask the mechanic to check the crank signal to the computer

That is almost impossible to "check". If there was a problem with that signal either the engine would not run or the computer would have reported the error.

and the signal from the computer to the IAC

Just because the IAC is getting a signal, doesn't mean that it is working correctly.

High idle can only be a couple of things. Sticking throttle, sticking IAC or a vacuum/air leak.

If you want to get your hands dirt a bit, while the car is idling, disconnect the IAC. The engine should immediately die or the idle drop off substantially. If not the IAC is sticking.