Low vacuum brake booster at idle

Hi,

It's about my car from my house and yard.

Passat Variant 3BG 4-Motion 1.9TDI with 131 hp engine, first registration 2002.

It has too little vacuum at idle for the brake booster, so that it feels like stepping on a stone, while otherwise everything is normal during normal driving.

Yesterday evening, I meticulously inspected the two-piece pipe from the tandem pump to the BKV from all sides for any cracks, and everything was fine. When pulling it out at the BKV, I could clearly hear that the vacuum was escaping there, so it seems to be sealed as well. The vacuum hoses for the boost pressure control, AGR, and so on are all new.

Now, the only thing left for me to check is the tandem pump. The connection there is also quite loose, but I haven't figured out how the pipe is attached there.

What do these guys mean?

Regards, Rüdi

Hi Rudi!

Check this out: /viewtopic.php?t=28847

Furthermore, the following tip from the above link regarding the connection stub of the tandem pump:

Mpire wrote:

Hello Check the connection piece in the tandem pump. This is made of steel and either cast or molded - depending on the pump manufacturer - and may be loose, which of course leads to air leaks. What many people don't notice is the apparent "routing" of the vacuum hose to the main control valve (BKV) in the spray wall; it is, in fact, not a "routing". This is a rubber connection fitting, into which the motor-side and the BKV-side lines are inserted once on each side. This seal can sometimes crack, become brittle, and allow air to leak into the system. Part number for the AVF/AWX in the 3BG is 8D0611743B. Price is approximately 5.28 EUR, depending on the retailer. It was already looking good, but the replacement fixed the problem. Greetings, Mpire

Best regards from Munich!

Thank you for the information. This little thing can be replaced occasionally, and it doesn't cost much.

Good evening,
I'm not really a fan of swapping out parts randomly.
Why don't you measure the vacuum at idle and at increased RPM, then I would also check with a vacuum pump to see if the BKV is actually maintaining the correct vacuum and not dropping.
Best regards, Thilo