I just dropped from about 45 mpg avg to like 25-30 mpg avg in one tank, no idea why and the car seems to be running as good as always. Nothing done to the car except an aftermarket exhaust thats a few months old. Hasn't had any tune ups or anything lately, and about due for an oil change, but i dont see anything making the fuel mileage drop that much so fast. I did run on my spare for a good 60 miles or so on that tank and then on unbalanced tires for another 60 until I got them balanced today(no garages open on sunday). I will see if gas mileage improves and report back. Any suggestions until then would be much appreciated.