air filter, oil change, plugs, maf.....make sure you don't have a brake that is dragging, no wheel bearing issues, tires aired up. not saying any one of those would cause that much loss but just do all the cheap maint and checks associated with mpg first. look under car and make sure hose going from filler to tank is dry but if gas was leaking anywhere you'd probably smell it or see stain on ground even if dried up. If your fuel filter was dirty enough to cause that much mpg loss i think you'd have a code. if your cat was getting that bad i think there would be a code. if your coils were bad you'd have a code. evap won't cause that much mpg loss but there'd be a code. how is oil consumption? do you go oil change to oil change without having to be adding oil?
