[CT Jack]

Seeing you have an FSI ignition module you need to check and reset your timing. You could be slightly too advanced. You might have a bad key switch that makes an intermitent contact when you turn it to the off position. As many of the threads are saying fuel gets pulled into the engine when you shut it down. If the key momentarily switches on it could cause a backfire. Case in point the FSI ignition puts out a hefty spark to the point where I have had my engine after it has been running a while actually start without the starter motor. Hopefully you allow your engine to come to a low idle speed before turning off the key. Cheers