sounds likely that you've found the problem then.

i had a calibra (or rather the missus did, i would rather chew my own testicles off than own an opel) that had a misfire from the king lead being a little loose on the dizzy cap. it happened coming home from the airport late one night so i put the lead back in and held it in place with a cable tie and it was ok for the rest of the way home. replaced the dizzy cap and lead and she drove it about for a while and we didn't think no more of it. a couple of weeks later it spluttered to a stop on the motorway on her way home from work. i went out to her and checked it out and it had a good spark at the right time and fuel was being injected so i couldn't work out why it wouldn't run. the aa bloke came out and he couldn't work it out either. it was only after he called his colleague who had dealt with a similar breakdown in the morning that he said to check the cat. got it home and removed the cat and sure enough it had melted solid, completely blocking the pipe.

so i cut the box open and removed the molten mess and welded the box back up and bolted it back up again and went to fire it up expecting it to run now. how wrong i was. removed the head and 2 exhaust valves had big holes in them, a couple of pistons were melted, the combustion chambers were melted - big mess.

and that was a 2.01 16V, not even a turbo engine.

so your mate better hope that it is just the cat and that he has caught it early. no need to buy a genuine audi cat, get a universal one that can be welded in, or better still, get one of the metal maxtrix 'performance' ones that are freer flowing. and have the lambda sensor checked before driving, as a knackered one will just melt the new cat.

bit of an essay, but hope the story behind it helps someone prevent major engine damage.