PLEASE HELP! horrible gas mileage

[monsta121]

So I have a used 2003 wrx with 91000 miles. Since I bought it the gas mileage hasnt been great (~19MPG). I changed engine oil, oil filter, transmission fluid, spark plugs, fuel filter, PCV valve and used seafoam along with lucas fuel injector cleaner. Nothing seems to help. I do from time to time get a P0420 code (cat converter). The car has a TBE with one stock cat on there where the O2 sensor goes. Also has a turboxs BOV. I am really confused and out of ideas. Only other thing I can think of is the wide-band O2 sensor. Although apart from the poor gas mileage the car runs great.

[Donkey]

Try cleaning the MAF sensor. The engine is not what 100% dictates gas milage. The biggest factors is the driver and tire pressure. Anytime your in boost your gas mileage is going to suffer. If your tire pressure is 2-3 psi low your gas mileage will suffer

[monsta121]

I will try cleaning the MAF today. Is there some kind of cleaner should use or should I just get some MAF cleaner from Autozone along with some q-tips?
I do open it up from time to time. However for the most part i dont see boost very often. On one tank i got ~280 miles. For a quarter of the tank I was driving very spirited. The rest of the tank was mixed driving very light throttle with shifts around 2.5k-3.0k. Any way to tell if it is the O2 going bad. My tires look properly inflated, but to tell the truth I havnt checked them with a gauge since i got a flat about 500 miles ago. Thanks for the input

P.S. Where did you get those top and bottom eyelids? I cant find them anywhere

[mudferret]

You can use: MAF cleaner, electrical contact cleaner, or NON-CHLORINATED brake cleaner.

Do not touch the wires in the MAF with anything, let the spray action do the work. Once you have your MAF removed; the wire you can see is the intake air temp sensor, the MAF wire itself is in the plastic tube.