2004 Ford Expedition hissing sound

2004 FORD EXPEDITION
45,000 MILES • 6 CYL • 2WD • AUTOMATIC
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CATHLEEN MEILE
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our ford started making a loud hissing noise,under driver side dash ,when brake pedal is pressed down hissing disappears but idle slows down and engine even has died twice please help so we know what we are talking about to repair shop
Oct 19, 2008 at 1:53 PM
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BLACKOP555
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the brake pedal easy to push down like normal?? stiffer then normal?? how long does the brake booster hold air after shutting of the vehicle.

disconnect and plug the vaccum line from the brake booster and push the brakes down hard, does that make the noise or make the idle change?
Oct 19, 2008 at 2:03 PM