I've decided to try some BG44k engine cleaner to help loosen the carbon deposits in my engine. It's not too bad but definately black and sooty. I've just filled up the tank so I'll be reporting back on my conclusions and watching my MPG and the general drivability of the car. This is in the A4 2.0 TFSi engine and I'm getting 31.5 mpg as my average at the moment. Anyone else tried it?