I have a 2006 Hyundai Sonata, 73,000 miles mostly highway, I bought the car used with around 20k miles on it, had it 1.5 years now. My fuel mileage has dropped on average 3-5 miles per gallon, doing 55 once yielded 36 mpg, now yields 30.5 mpg, there is a 1 MPG error rate between the computer and calculating it yourself. My real average, from tank to empty, the average is down about 3 mpg. My air filter is new, oil is Mobil 1 synthetic 5w20, no cel's.

I figured its time for a new fuel filter, does that dramatically affect fuel mileage? I know for a diesel engine I've experienced first hand the effects of a fuel filter that is full and needs changing, don't know how much it affects car. I don't want to get an induction service if I don't need it, what if its an O2 sensor going bad slowly? I'd like to figure it out without spending alot of money diagnosing the problem. Any ideas?

PS, 73,000 miles on what I believe are oem brake pads. I just had 4 Summitomo LSG's(i think thats them) put on, they are way better than the stock Michelins and cheaper too. The Michelin MXV4's do not allow water to pass from the sent tread to the shoulder, these do. While the Michelins were quiter, these Summitomo's provide WAY better traction and handling. No vibrations, smooth ride. Thanks.