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Discussion Starter · #1 ·
2001 beetle recently purchased. Occasionally after starting it runs rough and loses power assist to brakes. This sometimes happens while driving. Strangely, I turned off the engine, set the hand brake, restarted and it ran fine again.

I suspect a gremlin. Anyone have another idea as to cause and repair?

Many thanks in advance
 

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Power brake boosters are also failing on most of the German cars around year 13-14. Not saying this is your problem, but between the booster failing, the check valve at the booster failing and the vacuum hoses and sucking jet pump that many of the German cars use, anything is possible.

Smoke testing is a good idea to find vacuum leaks, BUT if the brake booster is bad, you WILL NOT see smoke leaking from the booster unless you bypass the booster input check valve and actually look under the dash for smoke.

Often you can actually hear the booster leaking and STFT values may be high or change when the brakes are applied.

In order to hear a leaking booster, you will have to turn off the main HVAC fan by running the fan speed all the way down manually, have the windows up and radio off. While stopped and idling listen for a hiss or fan sound from under the driver side dash. The lower hush panel will muffle the sound and may need to be removed to easily hear booster leaks. When the boosters first start to leak, you can apply the brakes and the hissing will drop in intensity and may even stop while the brake is applied. If you have an OBDII scan tool connected to watch Fuel Trims, you may find that the Fuel Trims drop back toward 0% when the brake pedal is applied and when the brake pedal is released you will probably see the STFT rise first.

To confirm if the brake booster is a problem the booster hose can be removed and plugged or the booster hose might be able to be pinched off for a test. The booster vacuum hose is molded and pretty stiff so it may be hard to pinch off.
 

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Discussion Starter · #4 ·
Thanks for the guidance

Thanks to both of you. "Fixing" the problem by usng the parking brake realy has me stumped.

I saw on another forum that the valve may be clogged. Their fix was to remove the valve, clean with carb cleaner and relace. I'll try this also.

I know as surely as the sun sets in the west that a repair shop wil diagnose as a bad valve AND hose and valve and say $500 to fix. Trying to avoid that.

Thanks again.
 

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Are you sure it was the hand brake fixing it and not just cycling the car off?

I would check the line for sure. Very common failure point on all mk4s. My husband's TDI Jetta had it crack, I had it crack on my GTI. He was able to just put tape around the crack in his line, I had to replace mine.
 
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