In brief, handed the S3 over to the girlfriend for 2 weeks and got it back, 60bhp down. lol.
Basically, was recording 234bhp on liquid gauge when I last drove it, didn't pull too bad. But noticed when I got it back it felt sluggish. Looked on liquid, only 171bhp. Checked Boost, boosting as normal (810mbar)... (N75 disconnected due to over boosting issues). Plugged n75 back in. Over boosting (1550mbar) and fluttering like a b!tch (normal). Overtook 2 cars, overboosted and power died twice (had to get off and on throttle to correct). After this, fluttering disappeared and boost stopped at 1540mbar and car pulled slightly stronger, but still not how it was. This only returned 197bhp. I know liquid is not accurate, but using for comparison purposes.
I know I have issues with this car anyway as in the turbo is hybrid and rest of the car is not supported, but why the sudden decrease of power!? Could it be a MAF issue? Fuel economy still seems normal. I haven't tried disconnecting the MAF yet.
Sorry to be a pain, but if anyone could shed any light, it would stop me frazzling my brain...