I think you are dealing with a vacuum leak in situation. The vents are actuated by vacuum. If there is a leak, what you described is what happens.
Check under the dash for disconnected, damaged, dryrotted. Vacuum hoses as well as under the hood. If you are lucky, you will hear a hissing sound from the leak with the engine running.
Let me know what you find.
Tuesday, June 22nd, 2010 AT 12:13 AM