2000 Ford Taurus

Engine Performance problem
2000 Ford Taurus 6 cyl Front Wheel Drive Automatic 57000 miles

When my car is running in either park or neutral, and the air conditioner is off, everything seems ok. RPM between 750-900 according to my OBD scanner. Now when I turn on the air conditioner the rpms drop low and cycles like that a few times, then the engine will die.
Now, for the weird part. When the car in in gear, and the brakes applied, the air conditioner is no longer a problem. The rpms hold steady after a very brief and small drop. As long as I am in gear, there is no problem. The problem is opposite of what I would expect, with the air conditioner being added load on the motor. Strange, isn't it?
August 18, 2009.

IT does sound like an IAC or throttle position sensor. HAs the check engine light come on?

For the past two weeks, I have viewed over one hundred(easily) posts concerning the IAC, and the TPS, how they work, symptoms, and how to test.
My $20 question is basically this: In all the posts, the idle/air conditioner problem happens when IN GEAR and idling.
My problem is this happens when NOT in gear. It's fine IN gear. When Not in gear is when I have my problem.I do believe it is the IAC or the TPS.I already have an authorized Motorcraft IAC and will install in about two weeks. That's the earliest I can get to it.
I have had a remote starter on this car for the past six years, and I haven't gotten into a cold car in all that time. I'll bet I have a well over a hundred hours idle time.
But, I really would like to get an explanation for my " problem only when NOT in gear" question.
I am not a car guy, I'm an electronics guy. Could it be that the computer knows when the car is in gear, and does something with the idle that it doesn't do when not in gear?
I really am looking forward to the conjecture concerning this, as it seems to be unique as far as the internet posts go.
Thanks again
Big Al Malik

Aug 19, 2009.
When in gear, the computer does know and sends a signal to idle the engine higher to compensate for the additional load on the engine, especially with the AC on.

Does that help?

It sure does help.I appreciate it a lot. Thanx, guys.I'll let you know how this plays out in about two weeks when I get around to changing out the IAC.
Big Al

Aug 19, 2009.
I forgot to mention that I get no codes at all.
Big Al

Aug 19, 2009.
I got around to installing the new IAC. When I started the engine with the AC on, the RPMs were still dropping, but not actually killing the motor. They did fall pretty low, tho. Then I moved the throttle cable, at the throttle body, with my thumb, and it seemed to be sticking closed. With a bit more thumb pressure, the butterfly in the throttle body would open.I did this a few times. It was definitely sticking.
I cleaned the inside of the throttle body. There was also quite a bit of varnish in it.I got it working smoothly.
The old IAC was had a good coating of carbon. When I cleaned it little pieces of carbon came out of it.I still used the new one, tho.
After cleaning the throttle body, everything works fine now.
Could it be that a sticking butterfly could cause the symptoms I was getting?
Also, does the computer have to " learn" anything after the work I did?
Just curious.
Thanks again for the help, guys. It was worth the
twenty bucks for the answer you gave me. It gave me the confidence to do the job myself. As I said earlier, I'm not a car guy.
All I spent for the job was $50 for the Motorcraft IAC
I bought from Rockauto and a few bucks for the throttle body cleaner.I have my own OBD scanner too.A professional car guy I know says I saved over $200.
Thankx again.
Big AL Malik

Sep 2, 2009.