I have posted here before on this issue, and changed the air intake filter for a Mini Mania JCW INTAKE AIR FILTER REPLACEMENT UPGRADE, and then turned the car over to the MINI dealer.

The dealer hooked the car up to their computer and could not find any problems, so returned the car with it still producing 14.5 mpg.

I'm going to bring it back to the dealer next week, to fix the problem, and think I need the advice from this forum to help the dealer identify the problem

Please post your thoughts!

Cheers.

 

Well, a couple questions:
What's your driving style? MPG is greatly effected by style and terrain etc...
What octane are you using? I've heard lower octane on an S will significantly lower MPG.
Is that MPG from your computer, or a real number from fill ups?
Have you noticed any other symptoms? Hesitation? Smoke? Anything puddling under the car? smells? You're at least 10 MPG down on the averages I've seen for an S, that gas has to be going somewhere.