I recently had the same idle issue with my 99 2.5L Contour.
When cold the engine would fire up, idle at about 1500 and then drop down to 0, sputter out and quit. Same thing when stopping for a light or stop sign. I found that if I kept my foot slighty on the pedal and "caressed" her a little bit, I could keep it running. Didnt' seem to get better as the car warmed up either. The problem started when the temperature here dropped to about 8 degrees F.
At first thought it was the upper intake gasket like Unisys mentioned or a vaccum leak somewhere else. I figured I would try the simple things first and put some Heet in the tank. (I heard this is not recommended though) and put some fresh gas in. I had about 3/4 in the tank to begin with. Well, the problem fixed itself within about 300 miles. Really not sure it there was water in the gas and it froze or if it is a gasket or vaccumm leak. It got a little warmer (about 25) and i can't test the problem again. I am kind of wishing for it get cold again so I can see if the problem returns.
Hopefully the fix is this simple for you as well.
Radioactive
