I wouldn't think a blocked fool filter correlates with poor fuel mileage. But I was wrong once before.

I suggest the first thing you need to do is check for error codes from the engine management computer. You can do this by building Arthur Dalton's code reader - use the search feature to find instructions. You could be dealing with a failed MAF or O2 sensor and not even know it. The car will run on a limp-home program in these situations. Driveability is poor and fuel economy is low when running in limp mode - sounds rather like your complaints.

- JimY