91 Lumina stalls when put in gear?

Last night when leaving work my Lumina started up fine...cleared the snow off the car giving it enough time to warm up and then when I put it in reverse it stalled...couldn't get it started again right away...tried starting it in neutral...didn't work...tried starting it a few more times...finally got it going and made it home but did it again this morning! What's causing this stalling?