2004 Pontiac Grand Prix No heat when idle

Welcome to the forum, no difference in air flow? It's just a temp issue? Does the engine reach operating temp? Are the heater hoses hot, when the problem occurs? You might need to have the heater core flushed. The flow through the heater core probably slows down at idle because the water pump slows down.

Thanks for the welcome. No difference in airflow at all. It is just a temp issue. The engine does reach operating temp but I haven't checked the heater hoses yet. Having the heater core flushed sounds like a good idea but I just had the coolant system flushed recently???? I thought it might be the thermostat??

If the problem only happens at idle and the engine reaches operating temp, I don't think the thermostat is the problem. Replacing it shouldn't hurt anything, but, I don't see it.

Thanks! I will do both and see what happens. I'll have the hoses checked as well. I'll let you know the outcome as I'm going to my mechanic today.

Have you found out wat was going on with your grand prix...Im having the same problem and it is starting to tick me off because I dont do much highway driving there for its always cold in my car..

I did find out what the problem was. I was told by my mechanic that one of the hoses had a small hole in it and was leaking antifreeze. He replaced all the hoses and the heat has been working fine ever since. That was last week so I suggest you check all your hoses. I haven't had them changed since I got the car in '05 so I think it was time. Let me know your outcome.