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Old 08-08-2008, 11:53 AM   #30 (permalink)
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Location: AZ
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First, I'd check the gauge on another car or put another gauge on yours. That will rule out a bum unit.

Finding a vacuum leak is a real bear of a project. Simple way to start is get a can of Carb Cleaner and squirt it at anyplace that air might want to get into the engine. Hoses, intake manifold gasket, brake booster, etc. If there's a leak, the RPM's will increase a bit.

If the reading is low, you can live with it. Maybe just how it's connected or a quirky gauge. The buzzing isn't too good, might want to check your valves. If one doesn't close properly you'll get a backflash from the cylinder that will disturb the incoming air.

Check out RWD - The Volvo Owner's Resource
Lots of help for your car.
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