[s-cars] No Heat at Idle?

[Brent Henry]

I have a 1995 A6Q 2.8, up until this year, the heater has been fantastic... 
very hot regardless of the temperature outside.  Which is great in Canadian 
winters.  However, this year, the heater blows cold air while the car is idling 
(even with the engine up to normal operating temp)?  Once I begin to drive, 
the hot air begins to blow just like normal?

What could be causing this?
Brent Henry.