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Car overheating when on heat

My 1999 pontiac grand am overheats when the heat is on, then goes back down to 200 when on cold. Car starts when you press on the gas otherwise its dies. Anyone know whats wrong with it?

If you have to press on the gas pedal to get it to start, could be a fuel injector is leaking and it needs more air to compensate for the extra gas that leaked out when it was sitting. If it is just that you need to press on the gas to increase the idle speed enough so when it starts it doesn’t immediately stall out, that could be the idle air control function. The overheating only when heat is selected is a weird one. Check the coolant level probably, as when heat is on the coolant that goes to the heater core is being robbed from the engine. If the coolant level is ok, that won’t be a problem, but if the coolant level is low I suppose it might.