1993 Nissan Altima

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?
January 18, 2006.

Fuel filter and decoke the throttle bore

Feb 8, 2006.