How do places like Jiffy Lube clean your fuel-injection system if you tell them too? My car's fuel injection system is probably dirty because my gas pedal doesn't have the smooth motion like our other cars have. I've put STP fuel injector cleaner down the gas tank the past 2 fillups and it's helped maybe a little bit when it was in the tank but goes back when it's all gone. Anyone know a more thorough way to clean it?