Check the vacuum connections at the "ball" in the driver's side fender(underneath, area between bumper and wheel), and at the check valves. If you have had a bad check valve for some time, you may have blown the rubber seal out in the vacuum switch that's located on top of the HVAC control unit(the control head which has the levers on it to select hot/cold and discharge position). If a vacuum line is disconnected for no reason, your check valves are bad and you need to order some replacements to keep boost out of areas it doesn't belong so it stops blowing apart connections. The check valves are cheap and still available from the dealer.
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