Nissan Repair: heater, blue norther, nissan maxima

Question
I have a nissan maxima 2003, with over 100.000 miles all of a sudden the heater works great as long as you are running down the road but if you idle or stop it turns cold and blows like a blue norther  WHAT'S UP////?
THANKS APPRECIATE YOUR TIME

Answer
Greg,

Sounds like the heater core has a restriction in it.  I would backflush the heater core gently.  Do not use too much pressure form a garden hose as you could blow the heater core.  It sounds like the blockage is overcome enough when you run down the road and the pressure is up and then it does not flow well at idle due to a blockage and the engine at idle.  I do not think this is blend door related.