I was getting around 11 mpg with mostly city driving with some freeway. Also no matter how I drove it was the same. I replaced my alternator and had the battery disconnected for several hours. Two tank fill ups since and I am getting almost 14 mpg now. Must of reset the ECU and modules. So you could start there.

I would check the air filter and maybe you are due for new spark plugs.

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2002 X5 4.6 Sold
Dinan CAI, TB, Mass Air, Stage 4 engine & tranny software, X-pipe
2004 745Li
1997 Ford Mustang Cobra Vert
1985 Mazda RX-7
13B-REW single turbo 60-1, Haltech, Meth injection, MSD Ignition, and much more
2008 Mazda Speed3 Hypertech Tune