Hi i recently bought a subaru impreza ej16 sohc non turbo and i think i have change everything on there such as filters, oil and plugs and plug leads but i still have bad gas mileage and i also notice it has this real slow response when i'm taking off, even when i'm driving and i mash down it hugs back and then takes off like a bat out of hell. What could be the reason for all this to be happening.