Some do seem to be more fuel efficient than others, and my 130 is no where near as efficient as Brians. 130s do seem to do better mpg than the 115s, but 30mpg is way too low, even if you're kicking the crap out of it.

Are the brakes binding? Either jack it up and spin the wheels, or see if any of the wheels are particularly hot after a long drive. Is the cat, or exhaust blocked? Is there a lot of black staining on the bumper by the tailpipe?