Ford Repair: 1995 Lincoln Mark VIII, lincoln mark viii, vacuum leak

Question
The heater only comes on when I am sitting idle at a stop sign, when I pull away from the stop sign the heater will completely go off.

Answer
check and see if air is coming out of defroster ducts when this happens if so check for vacuum leak underhood area first-check the vacuum hoses going into car-could also be a bad check valve in the vacuum system look for leak first if you dont find one follow up and i will find out where check valve is located.