my car has no good gas

[docB]

A dirty air filter does not do much to gas mileage because the mass air flow meter will not add more fuel than the engine computer maps will allow.

I am loosing mileage with winter, too. Longer warm-up, more rolling resistance from sloppy roads, the use of the rear window defroster and the air by the front defroster. Do add the winter air to the tires...

With a great car like the Yaris, all these things will kill mileage. With a big old V-8 pick-up, you just get the same poor mileage all year 'round.