1993 Other Oldsmobile Models engine stalls

I have a 1993 Olds Cutlass Ciera, front wheel drive and a "N" engine code. Most of the time it will drive really great. Sometimes when you pull up to a stop light and the engine dies. You restart and when you put it in gear again, it immediately dies again. Usually to get going you have to acellerate heavy and throw it into drive and sometimes it will run and other times it will die. I took it to a mechanic and he couldn't find anything wrong with it and it didn't act up on him. It doesn't act up all of the time, just some times. Can you please help me to try and figure out what might be causing this?