I am having a problem too of this kind. Mine is an old 1998 A6 Quattro. I usually get about 6 to 8 Lts per 100kms. Now I find it could go up as high as 14 Lts to the 100. This is what the computer is showing. It actually fluctuates a lot. The RMP would be the same and the speed the same but I could also see from my fuel gauge that I am consuming more than I should. This is based on the distance I normally travel and the amount of fuel I use.
Any help would be most appreciated.

Thank you.

 

I suppose the poorer gas mileage can be attributed to the use of corn based methanol (or ethanol, not sure which) added to the gasoline in Winter in some regions.
I wonder if your gas mileage would "miraculously" get better in a few months...

 

I do not know about the miraculous recovery but I did not have this problem last year.
Could it have anything to do with my transmission?

Thanks