I have an odd but continuing problem with my 2006 Buick van. (3.9L) It's -6 degrees here this morning. I started it up and let it run for almost half an hour before leaving. When I got in the temp gauge was at normal but all I had was cold air from the vents... until I started driving. As soon as the car was moving (or rpms up) I had all the warm air I wanted. This has been an issue with this car (bought it used three years ago) and it does the same thing with the A/C in summer. Everything works fine but you lose heat or cooling at idle. I've had it in to the dealer twice and all they do is back flush the cooling system but no lasting improvement. Any ideas, recommendations?