There are a lot of things that could cause a sudden drop in fuel mileage, so you may have to work on this one with patience. Here are a few tips that might help:
Check the catalytic converter to see if it's clogged.
Check inside the throttle body to see how gummed-up it is with tar-like carbon deposits. On older engines (mine especially), blow-by increases and causes a great deal of oil mist to exit the crank case and enter the intake plenum. Clean it out.
Replace the fuel filter. Any clog or partial build-up will affect fuel economy.
Check the intake snorkel (the hard plastic intake inside your driver's side fender, in front of the wheel well). Squirrels and other furry woodland animals have been known to store random shit in there, causing decreased breathing. I cleaned twenty spruce cones out of my friend's Bonneville and his fuel mileage went up about 40%.
Do a routine tune-up. New air filter, spark plugs and wires, new distributor cap and rotor.
Try the seafoam treatment seen on the link below. It worked for me:
http://www.youtube.com/watch?v=KhPsL-6VjLc
Check to see that your wheel bearings aren't blown, and check the brakes for seizing calipers, wheel cylinders, or e-brake cables.
I hope some of this helps...and I hope you find the problem quickly. I've been through almost every one of the things I've mentioned, so I know how frustrating it can get.
gas mileage
1990 5spd V6 Camry (Still kicking at 393,000km) 1991 Celica GTS -- Pappa needs a 3SGTE...and AWD for all this friggin' snow
Linear Mode
