I'm averaging 19.3 mpg, 50% city and highway, on my early 1999 6 speed. Stock size tires inflated to 70 psi, keep it plugged up on cold nights and about 2 minutes max warm up. I also don't let it idle for more than a couple of minutes unless waiting at traffic lights. Most of it is controlling your right foot. Leaving a couple of minutes early, keeping the RPM under 1750, smooth, slow starts from stopped will greatly improve your mileage.