The 2000 mountianeer starts and runs fine but shuts off

run the fault codes and look for faulty MAF/VAF sensors and ambient temp sensors.

There is a door in your air intake that is thermoststicly controlled
that is to remain partially closed until tge engine warms up.Thereby letting in cold air on a cold engine, causing it to run rough.

you have a bad idle air control valve. its job is to have motor rpm high until the motor warms up then turn it back to normal.

I have a 2000 pontiac grand prix with a digital climate control system. The heat quit working, it doesn't blow out any heat. Now that it is warm outside the air stopped blowing out any air. The digital temperature on the climate control is not correct. When it states that it is below 30 degrees on the ext and it is warm outside the air wont be cold. Once it starts going above 30 degrees the air gets colder. Today the blower stop working all together. Was told it maybe the climate control unit was bad. You can hear the door opening/shutting when you switch the temp from cold to hot. But there was no heat blowing out whatsoever in the winter time. Could you please give me your opinion on whether or not it is the climate control unit or something else?

if a clutch is bad it dont choose to be good in hot or cold, maybe it is the trans going bad as it warms up

have car scanned look at tps minnum should be around .50 at key on or running
also look at ect sensor if possible when ehgine is cold temp on engine should be within 5 degrees of outside temp
hope this helps.

check for intake leaks.

get a couple bottles of gas line antifreeze .. if you don't already use it and add it to the gas.

Robert

P.S. in minus 40 i don't even get out of bed... minus 23 here last nite... isn't winter grand

I was just reading the owners manual for my 2000 beetle and it says the diesel fuel has a problem with the wax separating from it below 40 degrees. Put the car in a warm garage and it will start.

Have a mechanic take a look at your throttle position sensor and engine idle sensor. Make him manually adjust them as opposed to just putting in new ones. It may require that you have to have a higher idle than normal. Your underlying cause is going to be that I am sure you have a lot of miles on your engine.