Thats no Moon, Thats a space station!
When you got the engine replaced did you get a new throttle body or use the old one?? as i had a similar issue that went on for ages till i got a new throttle body then all was good.
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