Define bad mileage?
I have a 98 GS4 (VVTi) and I get 19-23 mpg around town, and best of 29.4 and 30.3 mpg respectively on the highway.
I drive sane, don't hesitate to WOT it anytime I need to pass someone. But I have NEVER got worse than 19 mpg yet, that is in the last 30,000 miles.
I have 168k miles on the clock, stock 3.27 gears, I have run 0W30 Mobil 1, 5W30 synthetic Quaker State and just switched to Mobil 5000 5W20 (to test and see if fuel econ gains are real), if the 5W20 pans out I will go with Amsoil 0W20 before it gets too much colder here. I have NGK copper plugs (that need to be changed by now).
So makes me wonder what you have going on. When I was in the Springs I got better mpg with the MTBE gas, but I think all that has been pulled now due to water contamination. If you can get non ethanol gas, that helps everything.
I don't care if it is a V8, V6, I6, or 4 popper, reality is it takes xx hp to get a car down the road, so # of cyls isn't a big thing, size is, and we have small V8's. But my Fleetwood with the 5.7L LT1 got 16-23 mpg, even on E85 I never got below 15.
I would look and see if the O2's are bad (never ever change a rear O2 for fuel economy complaint), or look for engine not getting up to temp or a drag issue (worn or misaligned suspension). Or crazy driver's foot!
