My girlfriends car has been geting bad gas mileage lately, i replaced the spark plugs as they did need it bad, and we put an injector cleaner in the tank, it improved a little but still going bad. So we took it to a mechanic and they said two injectors were failing so they "cleaned" them and everything should be good to go. That was last week, today she went to start it and it started the spit and sputtered then died, and is now not starting..please help?