20vcqdriver
Did you manage to drive the car with vagcom connected?
Does the live data page show knock signal? or ignition advance values?
IMHO you should be looking towards the Injectors, I just saw you mentioned old fuel in a previous thread,totally different system I know but this wreaked havoc inside my fuel distributor
If an injector was partially clogged, it would not show a fault code unless the injector was electrically faulty and would cause a lean mix and detonation, the ecu tries to counteract this by reducing advance and boost, if it can't it goes into limp mode.
would expect to see a knock control fault logged though
suppose they could be tested on the rail, but I didn't recomend that
Professional cleaning and testing is safer.