Car keeps stalling, finally the check engine light has gone on what could it be?

all the mechanics said until the check engine light goes on they dont know what it is. of cause today is labor day and it went on so i cant get it checked till tomorrow. i have a 1999 G20 Infiniti with almost 86K miles on it. i am unemployed so a new car is out of the question any clue to what it might be?