i'm now only getting half the milage I got 6 mos ago out of my tank. on 2002 Chevrolet Cavalier

Don't know if it's 2.2L or 2.4, 2 yr old O2 sensor on front, 5 speed. I've always got 500km to a full tank, over last 6 months it's dwindled to 250km!

Asked by for the 2002 Chevrolet Cavalier
Air filter good shape? Had plugs installed? Check engine light on? Smell gas? Running rough? Good power?
An air filter won't impact fuel mileage. Top end power, yes but not mileage.
Oh really? Then why dont you just answer this!?!
Restricted airflow to the engine has no effect on fuel mileage, humm, humm,...
BS! Dont bother trying to explain, i have deleted this anyway!
Whatever. A gasoline engine runs at full power with the throttle open fully, and at any other time the throttle ends up being the greatest restriction to airflow into the engine, not the air filter. The computer through measurement of that air density calculates the required injector pulse width, and then uses the fuel trims to modify it to maintain optimum ratio's. So with today's cars a dirty air filter can actually cause an increase in fuel economy because under a heavy load it will simply make the engine run like you are not at full throttle. Now back in the 70's when we had carbureted cars and a specific study was done in France, that wasn't the case and the dirty air filter did impact the fuel economy then and there. That's just one study. There are plenty more.