Originally posted by LCX:
why am i only hearing it when blipping the gas while driving and not stationary?
Blipping the gas results in a sudden/temporary decrease in manifold vacuum -- opening the throttle valve thus tending to equalize the pressure/vacuum on both sides of the throttle valve. At stationary, manifold vacuum is maximal -- the engine is under minimal load and the volume of air at atmospheric pressure that is let into the intake is also minimal. So if there's a leak in the HVAC vacuum motor, it will be magnified when there's not a lot of vacuum "to spare" to 'cover up' the leak, i.e. circumstances when there is low manifold vacuum.
I don't have my Electrical & Vacuum Troubleshooting Manual handy, but someone more knowledgeable can tell us off-hand what kind of vacuum reserve system the Contiques have.  I don't remember seeing a vacuum reserve canister but then again I'm still learning about my Mystique.
Po
1995 Mercury Mystique GS: Zetec 2.0L I-4, CD4E
1978 Ford Thunderbird Town Landau: 351M (5.8L V-8), FMX
Coming in 2007 -- 1986 Jaguar XJ12 Sovereign: 5.3L High-Efficiency V-12, GM transmission
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