Can anyone explain why all the sudden my Fuel Mileage has dropped on 05 FX35 30k Grubbs 2 weeks ago did the Oil change and Fuel injection system clean and before all this I use to get a steady16 16.2 mpg Now it drops to 10.....11...sometimes 13 .I Just filled up with the expensive supreme gas <which i rarely used before> and its still the same.Is it possible that the dealer did something on the fuel injector cleaning to cause this?Car runs great with no system lights or warnings on.

No idea for sure.

It might be something unrelated that isn't triggering an SES light. Bad o2 sensor or knock sensor?

Sounds kind of fishy, like that fuel injection cleaning might have messed something up.

Couple consumer reports where is mentioned about fuel economyhttp://www.car-or-car.com/INFI....htmlhttp://w ... FI....html