As long as I am driving down the road my heater works fine but when I stop and idle my heater blows cold air. It is time for the timing belt to be changed and I was wondering if I should have the water pump changed also? Could that be causing the problem with the heating. My van has 205,000 miles on it. It is a 2002!
Try what I suggest here http://community.cartalk.com/posts/list/2134573.page, and see if this fixes the problem.