Turbo "pulsates", power brake booster failing

Hello everyone, I'm new here and I have a question or a problem.
I've already tried using search engines...

I'm currently working on a 1995 Passat TDI with 66 kW. The problem:
"Starting around 3500 RPM, the turbocharger begins to surge. This results in a pulsating effect: acceleration, then a drop in power, followed by acceleration again, then another drop, and so on." I've already inspected the vacuum hoses, but I didn't find anything.

2. The braking performance is okay the first time you brake. However, if you press the brake pedal a few more times, the braking pressure decreases. The pedal pressure becomes harder, meaning the vacuum booster no longer provides vacuum assistance. I've already checked the hoses and U-shaped pipes.
Result: The hose that runs from the vacuum pump towards the air filter was not properly connected on the air filter side. I reconnected it, but there was no improvement!

Does anyone have a tip for me?

Okay, here's the translation:

"Something else." The internal components of the intercooler seem quite oily - but I assume that's normal, OR IS IT???

Thanks in advance for your information.

Hi Manu!

ananga wrote:

(...) in other words, the BKV no longer has any negative pressure. Did someone give me a tip there?

Connect the vacuum hand pump with the pressure gauge, create a vacuum, and observe whether it drops. Possibly while wiggling connections, etc.

If no leaks can be detected, the pump must be inspected (using a vacuum gauge, observing the rate at which the vacuum builds up).
However, I strongly suspect there is a leak, as the necessary vacuum needs to be achieved first.

ananga wrote:

The internal components of the intercooler are quite oily - but I suppose that might be normal OR????

Yes, that's normal.

Please observe the forum rules; a question mark is sufficient.
Regards,
Guste.