After changing the air filter in my car, the MPG reading dropped significantly?

Last month I changed the air filter in my car because the old one was dirty. However, I immediately noticed a drop in the average miles per gallon-- it dropped by 6 (from 43mpg to 38 mpg). This seems large considering my driving habits have not changed. I still commute on the same route, at the same speed.

Is this normal after replacing the air filter? The old one was dirty and needed replacement.

If it matters, my car is a Honda Civic sport, 2006/7.

Secret. Orileys auto parts house brand are made by WIX. You must have another problem, changing a air filter will not change gas mileage that much unless it's completely stopped up and if it was stopped up that bad the car would not run well. Try cleaning the Mass Air Flow sensor.

Changing an air filter should not make your mileage get worse. You may have inadvertantly pulled of another hose of some sort, or is some other non related problem.

Were there any hoses connected to the air filter housing? Did you connect them back properly? Did you knock any wire connectors loose?

Make sure you closed the air box proprely. Also make sure you didn't break/unplug any sensors or forgot to plug back any wires you had to disconnect. If your car has a vacuum leak, you will definitely have a bad mileage on top of having a bad idle and maybe even a check engine light and misfires. Check all the vacuum hoses, sensors next to the air box such as the MAF and if you properly installed the filter and closed the air box.