I had the same problem with my car when i first got it then i checked the pipes and found one had a leak may want to double check and see if you are not leaking any boost. when the car is underboosting your motor is working to hard. remember with out the turbo its just a piece of crap. i got beat by a plymoth neon when i no boost at all lol i was getting like 18 i was getting sick of it. but fixed my leak and i was getting a average with some occasional boosting of 24 but when i went to oregon i got 32 mpg
that was so good made it there with gas to spare on one tank. running on 94 octane.
only 94 for some reason my car ran better with the higher grade. and remember each car is different. none the same.
