IAC replacement experiences on 2003 3.8L

I have a 2003 Windstar. 125K miles, done the isolator bolt fix a few years ago. No real problems. No check engine light.

Reason for the post: Idle was smooth except it would die when in reverse with the AC on and the steering turned all the way one way or the other. It happened to me trying to turn the car around in the driveway and working back and forth between two trees with the wheel turned hard. Foot off of the gas pedal, just the IAC running the engine. I'd call it max idle engine load. My wife said it only happens to her when she backs out of the garage. It never happens out on the road or in parking lots. So its appears to be cold engine related too.

I replaced the IAC with one from Advanced Auto, not a Motorcraft one. Idle was smooth until the idle speed needed to change. Then the speed would drop way too far, and then increase way too much before settling out. Example, put it in reverse. The engine would nearly die and then surge to 1500 rpm before settling out around 800 rpm or so. After a couple of tests I put the old IAC back on. I did not give the engine time to warm up. With the old IAC idle was fine except when in reverse and wheel turned hard.

Fuel pressure was marginal, barely 32 psi, but was also slow to move. It has been a long time since I replaced the fuel filter, so I put a new one on. Blowing through the old filter showed it was very restricted. Fuel pressure looked good at around 35 psi and responded quickly with the new filter. Pulled the regulator hose off and put it back on. Fuel pressure jumped up to 40 psi and back to around 35 psi.

Idle was better, I could not repeat the problem. So I decided to put the new IAC back on. Same as before, idle speed would nearly die and then surge to 1500 rpm and back to normal when I put it in reverse. I put the old IAC back on. I took the new IAC back saying it was defective.

Occassionally it is still dying on my wife when she backs out of the garage. I have not been able to duplicate it, but I'm leaning toward giving the IAC more attention. The old IAC had some carbon build up, but it did not look too bad. I did not clean it at the time because I was about to go out of town and did not want to make the problem worse.

My main question is: When replacing the IAC valve should I expect it to immediately run normal, or do I need to give the computer time to "learn" the new IAC valve? My second question is: Has anyone cleaned the IAC and made a problem worse?

I've got carb cleaner and MAF cleaner. I've thought about spraying the IAC down good with carb cleaner to clean it out, then MAF cleaner to finish the job. If that does not help the next step would be to put a Ford IAC valve on it.

I read a bunch of IAC posts but did not see one that matched my problem.

Thanks for the input.

Love that Daphne and Fairhope area! (Can't find me a great deal in a building lot, can you? ...on water.)

IAC's can be flacky. I think mine has served me all it wants too ... troublesome idling every now and then. You are correct in making sure gasoline pressure is not part of the problem ... also disable the EGR to make sure it is not a contributor. An "iffy" air leak can also be a problem.

Good luck!

After replacing any component I would disconnect the battery for 15 minutes so the computer can re-learn all of the optimal settings; every component has different specs and that's why most service manual will give you a range of correct values, that applies to the PCM as well, since each component is different it needs to "see" what's the best value for it.

Oscar.

I decided to go ahead and clean the IAC this morning. It did not make it worse, and may have helped. Idle is good. Its been hard for me to duplicate the conditions where it died before. Its not dying today. I'll have to give it some time before celebrating. Go to the beginning of the thread to see the original symptom.

A few suggestions for cleaning the IAC:
Have some pipe cleaners and Q tips on hand. Spraying with carb cleaner alone did not really do much. The carbon comes off pretty easy with gentle rubbing with pipe cleaners. I gently pushed the valve open to give plenty of room for the pipe cleaner, and then rubbed it around. Periodically I would cut the end off so that I had a clean end to work with. Spray it occasionally and rub some more. Cleaned the larger parts of the body with Q tips. Got things pretty clean. Then I gently pushed the valve towards closed and cleaned the stem. Sprayed more carb cleaner, and followed up with MAF cleaner since it leaves no residue behind. Plan on being generous with the carb cleaner so you can "hose it down good."

The last piece is humidity related. Those of you in Arizona probably won't have this problem. Spraying the IAC down with carb cleaner and MAF cleaner cools the IAC body down a bunch. With dew point here around 78 deg, I quickly had water condensing everywhere. Periodically I would stop and sit it in direct sun for about 5 to 10 minutes and let the body heat up to dry out the moisture. A big hint: don't do this on a rainy day unless you want to use a blow dryer.

Using the pipe cleaners and Q tips helped a lot. As for performance, the car cranked up perfect first time and is idling fine.

Further update. Cleaning the IAC valve did not fix the problem. Went dead twice yesterday. May have even made things a little worse. At one point yesterday my idle speed was above 1500 rpm.

Went ahead and spent $131 at the Ford dealership. They had to get it from the warehouse, but had it by lunch time today. Everything seems fine.

So cleaning the IAC was a waste of time in my case. Now just have to see if it still goes dead occasionally in reverse.