What are the causes for losing gas mileage? Besides driving fast.

I normally get 15 mpg. But lately i've been getting @ 12 mpg. I've checked my tires and they are fine.

Any experience on this...
Thanks

 

Dirty air/fuel/oil filter(s) or just plain dirty oil. Old spark plugs/wires. Basic maintence basically. Might try running some fuel system cleaner as well.

 

ok, I just changed my oil two weeks ago, my Bonez breathing element is still clean and I've got less than 7K on my current plugs. My Magnecore wires are less than 2 years old.

I'll try a fuel system cleaner, what do you recommend? Periodically I run MMO.

Any other ideas

 

*bump*

 

change O2 sensor
check your compression
run lots of fuel system cleaner and clean throttle body

 

Stick with MMO.

Check the resistance of your plug wires. Are you using di-electric grease with your plug wires?

Check your engine codes.