horrible MPG Options

[xs94st]

hey guys..jus want to know what could cause horrible mile per gallon averages. i've been slowing down n driving 65-70 n still my gas just seems like it just drips out as i'm driving along. i filled up n i'm at about 1/4-1/2 a tank and i've only gotten about 140 miles. im gettin an average of 240-260 miles per fill up. yea.

i have a CEL because i have yet to install my 2nd O2 sensor (i have everything, but i just dont have time rite now to work on 'er)

i changed my oil early and wont need to be changed until the end of december.

i purchase 89 octane gas when i fill up.

new tires in front with 50-60% tread on the rears

i don't use any fuel additives, just the GUMOUT injector/fuel system cleaner when i change my oil.

original spark plug wires, NGK plugs

i use 10w30 royal purp synthetic oil

K&N oil filter


what tests can i run to check for vacuum leaks n such? would those cause bad MPG? anything else that could be checked?

i've read most of the MPG threads n they weren't much help because the stuff i wanted to ask were not there and were not specific to my car, so please avoid recircling me back there. i'd rather have someone help me out in regards to what i have written and requested, not anyone else.

thanks guys

-x

[GriffGirl]

Definitely replace the wires, cap & rotor, that'll make a huge difference. Also make sure your air filter is clean, that will also make a huge difference.

[Sinyk]

My gummed up EGR has been causing my mileage to drop. That and cold weather.