Thats no Moon, Thats a space station!
Yeah your brother leons maf could well be faulty as the more air flowing in the 80mm TIP may just be too much for it and is scrwing it up. best way to check this is with VCDS or just unplug the MAF and see if it runs better if so new MAF and all should be good (also check for boost leaks too)
If you do get a new MAf dont forget you can get a discount for returning your old faulty one in exchange wherever you buy it from
Audi S3 8L BAM 225 2002 - Ming Blue : Silver Heated Leather, Armrest, RNS-E & Bose, Alloy Mirrors, Gunmetal 18" RSTT`s, Sunroof, Cruise, AutoDim Mirror & usual S3 extras.
Mods : Revo Stg 2 & Select+, FMIC, 3" DP & 200 Cell Cat, 007P (New Piston), Jetex Filter & 80mm TIP & Heatshield, LED Sides & Fogs, Gen VW Aero Wipers, Full Powerflex Kit, Lowered on AP Shocks & Springs, 15mm Front & 20mm Rear Spacers, N249 Delete & Catch Can, AP TVR 4Pot Brakes & DS2500`s, Sachs DMF & Carbon/Kevlar Clutch