You either have a vacuum leak or a vacuum hose to the HVAC that has collapsed. Check for leaks under the dash. With the engine running, you may hear a hissing sound. Also, check under the hood for the same thing. Follow the vacuum supply hose from the control through the firewall and to the intake. I have not only found them dry rotted, but collapsed.
Let me know what you find.
Tuesday, June 1st, 2010 AT 10:19 PM