My Service engine soon light came on last thursday so I took it to Autozone to have the OBD reading done. It spit out a code similar to 02506 - "emissions control or small leak" it said. recently it stalled out on me while coming to a stop and my mpg have gone down, especially while idoling. could this mean there is a leak in the exhaust or perhaps I need a new O2 sensor? any suggestions?