Vacuum Brake Booster: Low Assist at Idle

Hi there!

Here's the translation:

"This is about the car belonging to my house and groundskeeper."

Volkswagen Passat Variant 3BG 4-Motion with a 1.9 TDI engine (131 hp), first registration in 2002.

It has insufficient vacuum at idle for the brake booster, which means you have to press the pedal very hard, but otherwise everything is normal during regular driving.

Yesterday evening, I meticulously checked the two-part pipe from the tandem pump to the brake vacuum booster (BKV) for cracks on all sides – everything was okay. When pulling it out at the BKV, you could clearly hear the vacuum escaping, so it seems that part is also sealed. All the vacuum hoses for turbocharger pressure regulation, EGR, etc., are new.

"Now, it seems like the tandem pump is the only option left for me. The connection there is also quite loose, but I haven't yet figured out how the pipe is attached."

What are these guys talking about?

Best regards, Rüdi.

Hi Rudi!

Look at this: https://community.dieselschrauber.org/en/viewtopic.php?t=28847

Here's another tip from the link above regarding the connection stub of the tandem pump:

Mpire wrote:

Hello. Check the connection stub on the tandem pump. It's made of steel and either cast or pressed in – depending on the pump manufacturer – and it might be loose, which could cause air leaks. What many people don't realize is that the so-called "connection" of the vacuum hose to the main control valve (BKV) in the injection wall isn't actually a direct connection. This is a rubber connector with a sleeve design, into which one cable from the engine side and one cable from the battery control unit (BCU) are inserted on each side. This fitting is prone to cracking, becoming brittle, and allowing air leaks into the system. The part number for the AVF/AWX engine in the 3BG is 8D0611743B. The price is approximately €5.28, depending on the retailer. Just replace it; my one in the A4 looked fine on the outside back then, but replacing it fixed the problem . Greetings Mpire

.

Best regards from Munich!

Thanks for the info; this part can be replaced occasionally, and it doesn't cost much.

Evening.
I'm not really a fan of constantly replacing parts.
"Please measure the vacuum pressure at idle and at higher RPM. Then, use a vacuum pump to check if the vacuum control valve (BKV) maintains the correct vacuum level and doesn't drop."
Best regards,
Thilo