Intermittent vibration when stopped

Ihave1 · 05-23-2011, 07:11 PM

When I come to a stop after the car has heated up I am feeling a short .5 second vibration in the brake pedal. It almost seems like something is charging up or a clutch engaging in the engine bay. It happen with the AC off, transmission in neutral, and will happen about every 30 seconds to a minute if I let the car idle. I usually notice it while waiting at stoplights with my foot on the brake.

Believe it or not it sounds similar to "The Bloop" but with more of a vibration tone. Maybe that's the explanation?

Any ideas? Of course the dealership wasn't able to hear anything when I had them look at it.

Turbolader · 05-23-2011, 08:07 PM

shot in the dark here, but it could be the vacuum pump. If you can feel it in the brake pedal, it's more than likely a small fluctuation in the vacuum available to your brake booster and you're feeling the small difference in assist in the pedal.

Normally engines have enough vacuum at idle, but I read somewhere that the vacuum pump runs in our cars at idle, and at WOT because of lack of vacuum.

If it isn't that, then maybe it would be something in the ABS unit, but I would highly doubt your problem is there because you would get a service light if the ABS relays kicked off without any motion from the wheels.

05-23-2011, 07:11 PM	#1
Ihave1 Private First Class 42 Rep 159 Posts Drives: 2008 135i Join Date: Jan 2011 Location: NC, USA iTrader: (1)	Intermittent vibration when stopped When I come to a stop after the car has heated up I am feeling a short .5 second vibration in the brake pedal. It almost seems like something is charging up or a clutch engaging in the engine bay. It happen with the AC off, transmission in neutral, and will happen about every 30 seconds to a minute if I let the car idle. I usually notice it while waiting at stoplights with my foot on the brake. Believe it or not it sounds similar to "The Bloop" but with more of a vibration tone. Maybe that's the explanation? Any ideas? Of course the dealership wasn't able to hear anything when I had them look at it.
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05-23-2011, 08:07 PM	#2
Turbolader The Fat Stig 11 Rep 274 Posts Drives: 2010 135i Join Date: Dec 2010 Location: 2003 Stg 3+ SRT-4 iTrader: (1)	shot in the dark here, but it could be the vacuum pump. If you can feel it in the brake pedal, it's more than likely a small fluctuation in the vacuum available to your brake booster and you're feeling the small difference in assist in the pedal. Normally engines have enough vacuum at idle, but I read somewhere that the vacuum pump runs in our cars at idle, and at WOT because of lack of vacuum. If it isn't that, then maybe it would be something in the ABS unit, but I would highly doubt your problem is there because you would get a service light if the ABS relays kicked off without any motion from the wheels. __________________ Philippians 1:20
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