I too have the same problem on my 02 tdi 130
I bought the car as salvage and have since repaired it and had the vosa vic test
When I bought the car it been in a salvage yard for a few months and the plenum chamber was full of water , I drained tthis ( unaware of the inherent problems)
But I have only today experienced the problem for myself ( on a hill with my wife an child in the car)
Am I able to claim for this directly from Audi ?
And where is this electric vacuum pumps people talk of as I cannot see obe but there is a fuse in the fusebox marked as 'brake server' (5amp fuse 4)
I will carry the repair out myself If need be as I do my own repairs but am very disappointed at Audis apparent lack of concern regarding this potentially lethal design fault !