Heater works if running down the road or sitting still and rev-up the engine.

Update from Jan 10, 2011: The heater core was bad and replaced.....then the water pump had gone to pieces too.....now there is abundant heat at all times

Update from Jan 10, 2011: The heater core was bad and replaced.....then the water pump had gone to pieces too.....now there is abundant heat at all times......the core was most difficult to replace