Why does your car intermittenly die out when you start it in the cold weather?

a little bit of more information... i drive a 1997 maxima and sometimes it will start right up, and others it will start up and idle down and die like instantly unless i hit the gas and rev it a couple times. I got it checked out like 4 times... my mechanic put a cold start solenoid in it, cleaned all the valved, put 2 cool temp sensors in it and it still has the same problem...anyone have ideas?