I can't believe no one has asked about this yet...here goes. I am working with a '98 323is high mileage vehicle with good maintenance schedule. I have gone from 24-27 MPG a couple months ago to now around 19-20 MPG. This is NOT correct and I do not know why. Can someone help? O2 sensors good, no codes, stock air induction (want to change eventually), cylinder compression good and consistent, no fluid leaks, newer plugs, newer complete cooling system overhaul (fluid, pump, leaks), new fuel filter, did not run fuel system cleaner yet... winter months have begun here in WI...a factor w/ different gas formulations at the pump? possible bad wheel bearing up front - does this factor?...running on winter tires (Dunlop Wintersport D3) with a minor bent rim - does this factor? ...auto trans needs fluid/filter replace - does this factor? Why am I losing 5 mpg?