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Old 09-09-2009, 04:51 PM   #1 (permalink)
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I cannot pinpoint a specific leak, seems to be everywhere. I replaced the idle air sensor gasket with a silicone gasket, fixet the leak there. But there seems to be multible leaks on the hose that comes off the air filter housing. But my question is would these vacuum leaks have anything to do with the brakes? When at low rpms the brake pedal goes to the floor and barely stops. Any ideas?
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Old 09-10-2009, 10:14 AM   #2 (permalink)
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I didn't catch your previous posts so bear with me here. It seems you're having multiple vacuum issues. This post mentions multiple leaks on a line from the breather box. These leaks are outside of the throttle body and should not affect idle or cause an major performance problems. You also mention a low brake pedal condition at low rpms. Your engine should develop its' highest vacuum at idle or deceleration so the low pedal should be the result of maximum boost.

The brake power booster is essentially a large vacuum servo. It is basically a vacuum tank with a diaphragm in the middle. When you step on the brake pedal it causes a valve close off the diaphragm and open the back of the tank to the air. Atmospheric pressure pushes the diaphragm in the same direction as the pedal push. I explained all this so that you will understand the next part.

Your post said you could hear a constant vacuum hiss. It also said that your brake pedal goes down further at low revs. It is possible for your vacuum booster to fail if that valve fails or the diaphragm splits. I don't know if you are having any problems with idling but it is possible for the booster to fail without causing noticeable idling problems.

If your booster is functioning properly your rear brakes may need attention and that could cause the drop in pedal height. If the brakes are severely out of adjustment, or if there is air in the system, the master cylinder could be near the end of its' travel range.

Sorry for the rambling post but I see a potential safety issue here and I don't have all he information to work with.

Good luck, Popeye
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Old 09-10-2009, 11:11 AM   #3 (permalink)
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I am having idling problems, it will not idle. It usually shuts right off whenever I come to a stop, unless I put it in neutral and rev it. However sometimes it will rev up on its own to about 3000 rpms it will hold that for 30 seconds and then shuts right down.
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Old 09-11-2009, 11:07 AM   #4 (permalink)
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This does sound like the vacuum booster is leaking air. Can you hear the hiss inside the car (under the dash above the brake pedal) if you don't step on the brakes? If you can hear it, the booster is bad.

Remove the vacuum hose from the brake booster and block the opening a piece of tape. Start the car and see if the idle is stable. If the booster is bad, the car should idle normally (even in gear) with this hose blocked. Any good manual will tell you how to R&R the booster.

You can drive the car with the brake booster bypassed but you will not have any power assist so I don't recommend it.

Keep us posted.

Good luck, Popeye
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Old 09-11-2009, 12:49 PM   #5 (permalink)
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QUOTE (popeye @ Sep 11 2009, 11:07 AM)
Quote:
This does sound like the vacuum booster is leaking air. Can you hear the hiss inside the car (under the dash above the brake pedal) if you don't step on the brakes? If you can hear it, the booster is bad.

Remove the vacuum hose from the brake booster and block the opening a piece of tape. Start the car and see if the idle is stable. If the booster is bad, the car should idle normally (even in gear) with this hose blocked. Any good manual will tell you how to R&R the booster.

You can drive the car with the brake booster bypassed but you will not have any power assist so I don't recommend it.

Keep us posted.

Good luck, Popeye[/b]
I cannot hear the hissing inside the car, stuck my head under dash. The hissing sounds like it is coming from the idle air sensor but I fixed that leak so I dont know what the heck it is.
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Old 09-11-2009, 01:18 PM   #6 (permalink)
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My car (2001 Taurus)did something similar to that. My vacuum leak was the 90 degree rubber connector for the PCV valve.
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Old 04-19-2010, 11:15 AM   #7 (permalink)
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QUOTE (Rick2 @ Sep 11 2009, 12:18 PM)
Quote:
My car (2001 Taurus)did something similar to that. My vacuum leak was the 90 degree rubber connector for the PCV valve.[/b]

DITTO
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Old 04-20-2010, 08:58 AM   #8 (permalink)
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Richmo,
If your vacumn leak is as bad as you say, take a piece of rubber hose and hold one end to you ear and use the other end like a stethoscope. It should roar like a jet plane. Caution on driving with your booster disconnected. I did that once to check something out and had to press so hard I came off the seat to stop. Got my heart going good. Like Popeye said just disconnect the main booster supply line and plug it, if it runs good then you have your answer.

ED
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Old 03-03-2011, 01:49 PM   #9 (permalink)
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The rubber hose holding one end to your ear and use the other end like a stethoscope was the best that worked for me in finding a leak in what is called "Vacuum Manifold" and it is located on the firewall right above the master cylinder in my 1999 Ford Taurus. The plastic manifold box had a hole. Cost $52.00 at the dealer.

Problem solved and my yellow warning light did not show up anymore. What a nightmare.
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Old 03-03-2011, 10:40 PM   #10 (permalink)
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^ Glad you got it fixed, but remember next time you can get that vac. tree (manifold) at a self service salvage yard for $1-5.
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