My 1993 nissan altima with 127 000 miles will start up fine, but irradicaly stall while i'm waiting at a light or, not giving it gas for a while. It actually stalled on me while I was slowly merging onto a freeway, but started up fine right away. Also if I am idling and just put it in neutral and give it gas, I can prevent it from stalling. There hasn't been a pattern at all and it hasn't stalled for my mechanic. I have had the carbon cleaned out and the fuel injector was replaced a couple years ago.I don't now what else could be wrong with it, and my machanic seems to be stumped as well. Any suggestions?