could be going into "limp" mode..the ecu basically goes into a safe mode when it detects too much knock. Try disconnecting your battery for a few minutes and and then re connecting. drive it off boost get some good octane booster Lucas or NF go to your nearest maxol and fill up on e5(not e85 e5 i there standard pump fuel in most maxols now) put some booster in the drive in on boost again and see what happens.
The B4 is designed to run on 100 octane fuel from the pumps in japan with the lowest recommended as 98, all our fuel is 95 octane with the exception of maxols e5 which is claimed to be 99.2 but is probably around 98.
I would plan on getting your car remapped, this basically involves a tuner hooking up his laptop to your ecu and matching your air fuel mix and engine timing to suit the fuel you are using, it makes your car safer and transforms the performance, you can get it done now including a an uprated fuel pump for around 850 euro.
HAve a go at that anyway and come back and let us know how you got on