I tuned up my Civic cx and ever since unless I'm drugged the car is getting way worse fuel mileage. I replaced the fuel filter, plugs and distributor cap (screw is stripped on rotor, I'm working on it.) I commute 160 miles per day so I really notice the difference in fuel consumption. Could the problem be a bad filter? The car seems to be running fine, doesn't hesitate or anything and no smell of fuel. Any suggestions? I'm thinking I should try another filter? Thanks.

 

I doubt a new filter is the problem, especially if the car doesn't hesitate and stuff. Did you put the correct NGK plugs in the car?

 

You could have possibly gapped the plugs incorrectly, and you could also have a O2 sensor. I would also suggest finishing up the tune-up w/ wires, rotor, coil, and O2 and see how you're doing then.