92 Taurus won't idle, stalls when stopping

1992 Ford Taurus 3.0L Auto. (Approx. 160k Mi.)

Here is the situation:
A few weeks ago the 'Check Engine' light started coming on everytime I rapidly decelerated (such as at a stop light) from 45-50
MPH. Since it only came on (with a 5 second duration) occasionally, I figured it was probably an emissions component and I was planning to check the codes later when I got time. Well the light began coming on more frequently, not just at 45-50 but eventually everytime I decelerated. I decided I would check on it this past weekend but 2 days prior when I went to pass someone and vigorously downshifted to do so (more than I usually do) it stalled the next time I came to a stop. When I restarted, it stalled again. I immediately parked it in a nearby lot (one foot on the gas and one on the brake) and disconnected the battery (for awhile) to clear the KAM, hoping it would possibly correct the problem or else store a fresh set of codes. When I reconnected the battery and restarted, the car acted the same. As long as I don't let off the gas, either idling (in park, neutral,
drive, etc.) or slowing completely to a stop, it won't cut out. The engine runs smoothly when not idling. If I gradually release the gas pedal (with no load) it will idle very delicately almost cutting out. Also the when first starting the engine will 'hunt' for the correct idle when I not racing the engine, but only when the engine is cold.
NOTE: Up to this point I've not had any problems like this nor has the 'Check Engine' come on since purchasing the car over 2 yrs. ago.

-I tried pulling the codes using the self-test through the 'Check Engine' light (counted flashes). All I could get was 634-MLP Sensor Voltage Out of Self-Test Range after a series of 6 single flashes (1/2 second pause between each and a 1 second pause after the first 3 of the 6).
-I read online of a dirty Idle Speed Control being typically the problem. I don't have this but I do have an Idle Air Bypass Valve and it was quite dirty so I cleaned it with carb. cleaner. (I also tested it with an ohmmeter and the readings came up fine.) This didn't solve the problem though.
-I cleaned the Air Charge Temperature Sensor (it was full of black gunk) and checked the readings with an ohmmeter but no problem found. This again didn't solve the problem.
-I found how to clear the codes completely (not just by disconnecting the battery) and drove around for a few miles. When I
checked the codes again (KOEO) it gave me 522-Vehicle no in Park or Neutral during KOEO test (2 times), a pause, one flash, another pause, then 634-Sensor Voltage Out of Self-Test Range (2 times).
-I also tried the KOER self-test procedures but all I received was continuously on 'Check Engine' light.
-I looked online for the MLP (Manual Lever Position) Sensor and found it had other names: Transmission Range Sensor and Neutral Safety Switch.
-I tried getting a replacement (under the name "Neutral Safety Switch") from Advance Auto but it had the wrong connector piece. After looking and looking and cross-referencing they couldn't find the exact replacement. As a result I'm richer but still with the old part.

Any thoughts or directions?

Your symptoms sound very much like a bad Idle Air Bypass Valve.....you may need to replace it.

Cleaning sensors.....Mass Air Flow sensor (if you have one) with nonresidue electrical cleaner.....and making sure that you do not have any vacuum leaks are other things to check out.

Here is what I've done so far:
I took the Idle Air Bypass Valve off and connected it to a 12 volt supply. It moved a very, very small amount. I tried reversing the polarity and it sparked and did nothing. I measured the current and resulted in 1.3A when it responded and 5+A when it sparked. When I measured the resistance, as mentioned earlier, it read 10.1 ohms (it might have been Kilohms, but either way it was in the tolerance range of the manual) either direction. This was approximately what the new one read in the parts store as well.
I reinstalled the valve and left it disconnected. The idle problem was still the same as before.
I loosened the valve so that it basically just rested on the engine and restarted the car, yet the idle problem was unchanged as well as the engine performance.
I took a screwdriver and gently wedged it between the engine and the valve so that a 1/4" gap existed and started the car. This time the car ran terribly and the idle problem didn't change.

I haven't had time to clean out the MAF Sensor since it got too dark. I may try this soon.
My thought is that if the problem suddenly happened only some warning (if that was what the flashing light was refering to) it would seen to be a component that went bad rather that a build up of dirt. (Of course, my thoughts tend to be out a bit in left field :D .)
I didn't have any related performance problems prior to this and the fuel economy (which has been good) hasn't deviated either.

Anyway, my question is how much is the valve supposed to move?

I do not know how far or how fast your Idle Air Valve is supposed to move..... Sorry.

You could check on Autozone repair guide for instructions on how to find, disassembe, and reassemble items, such as your tramsission range sensor, MAF, and clean / replace as needed.

You can check www.partsamerica.com for parts also.....they are Checker, Advance, and a few other chains......and you can check for in store stock...before you drive to the store.

Also, www.rockauto.com is another good parts source.

I finally decided to take a chance and buy the Idle Air Control Valve. After installing it and clearing the memory/codes, the car started up and held the idle beautifully!! :D
What's even better is that it solved some symptoms that I thought was from the tranny going bad! :D
(Although the two codes previously mentioned still show up on the self-test routine, which I'll post as a new thread later. )

Thanx to those who responded!