my brother has an 02 gt and he's having some issues with it. the idle is revving up to around 2k he said, then falling down and revving back up again over and over. the car is bone stock other than a k&n intake and some weld in mufflers. i suggested that he check the mass air so he cleaned it, and then decided to replace it bc the guy at autozone told him his was bad. he did not buy it at autozone, he bought a factory ford one. it did not fix the problem. what exactly is the fuel metering gauge, and what does he need to do to fix this thing as cheap as possible while still doing it right. this is his daily and he just had a kid so he's low on cash.