91 buick skylark dies when put in gear

[Nicole]

So last weekend I bought a 91 buicl skylark form my sister's father in law. He said it was in good condition. I test drove it seemed fine--"only" 100, 000 miles on it.
Bought the car drove it back to my sister's house. Decided to leave for home. Drove about 15-20 minutes came to a stop sign and as soon as I tried to come to a complete stop the car died. It starts right back up but as soon as you put it in gear it dies again.
If you let it cool down and sit for a while it will be fine and you can stop without it dieing--but once the car "warms up" or you drive it for a while it dies again when you try to stop.
We flushed out the system and replaced the fuel filter and put a new battery in it....

Any other ides about what could be wrong with it?

 

[LJ]

If it will run (with your foot on the brake) if you give it a "little" throttle before you put it into gear then it is the IAC or idle air control valve that is stuck or burned out (The IAC is like a miniature throttle to maintain idle speed).

You can confirm that the IAC is at fault by putting the Air Condition on with the engine in neutral (cold or hot). If the engine slows down or really slows down and nearly kills, it is the IAC (about $40-50 and is easily changed, at least on the V6 engines)

If the engine does not slow down when you turn on the AC (if the compressor is working), the IAC is good.

You have a switch connected to the shift lever that activates this IAC when you shift into gear. It cause the IAC to open up a little to keep the engine at the same speed. It is sometimes called the neutral safety switch but it performs another duty, it sends a voltage to the computer and subsequently to the IAC when not in neutral or park to keepthe engine at the same idle speed.

You stated that "If you let it cool down and sit for a while it will be fine and you can stop without it dieing--but once the car "warms up" or you drive it for a while it dies again when you try to stop."

The engine is kept above idle when cold by the IAC and goes to a normal lower rpm when the engine warms up.

It sounds like the neutral Safety switch is the first culprit if not, then it is the IAC.

Have someone test both.

After starting it cold, it will run at a fast idle. After a few minutes the RPM will slow down gradually. If it keeps running for a 15 minutes to a half hour you can put it into gear and then backinto neutral every minute after starting it to see if it will at some point start running at a slower and slower rpm so that eventually when you put it into gear it will run too slow and it stops. That says it is the neutral safety switch that is not working.

However if when you start it cold, and it does not run at a fast idle but the same rpm as it does 15 minutes later in neutral (and the AC slows it down noticably cold or hot) then it is the IAC.

Any friend who is a partial mechanic can figure this out with these instructions if it is too complicated for you. Print this out for a competent mechanic to read and try.

Let me know what you find?