I drive a 1999 GTP. Engine has 105k miles. U-bend delete and CAI are the only modifications. I run conventional oil. I have been paying close attention to my mileage since the fuel prices are on the rise again. My past 5 tanks have been averaging a mere 17.6 MPG. That is 85% highway driving at 60 MPH with very little traffic. The mileage was calculated by dividing the mileage on the trip odometer by fuel used, not using the information center. The engine performs flawlessly and runs great. No rough idle or anything. I have changed the fuel filter, cleaned the throttle body, replaced plugs and wires, scanned for codes, checked for fuel leaks, checked fuel pressure, checked compression, and checked tire pressure. Everything was normal.
With that being said, from the research I have done on this site, the mileage I am averaging is not normal. Does anyone have any suggestions on what I should check next? Last summer I was averaging 25 with the same driving habits. Also, can anyone offer any suggestions to improve fuel economy? I have heard switching to synthetic oil could improve economy. Would probably be a good idea to switch anyways with 105k miles. Thanks!
