Go to autozone to get your codes pulled for free. Even if the car comes up with no codes, clean your maf and refurbish the k&n. Then run a tank of gas and see what happens. If no luck there then replace the plugs, wires, cap and rotor, and maybe the coil, just really give it a little tune-up. And if all this come to no gain in mpg then buy two new O2 senors and replace those and that should fix the problem if nothing else does.
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