One day my check engine light came on and I had found my fuel mileage to have gone way down. The check engine light was was found to be 7 codes all relating to vacuum pressure problems, pressure drop between turbo and Diverter vave, fuel lean codes and a few others. I took it to the dealer and they told me things I dint care about at all like the airbag had a old fault code and the battery voltage was low blah blah blah, this went on for a few months and finally one day I went poking around and found a cracked vacuum t fitting hiding under the intake manifold, cost me all of 7 bucks to fix and the car worked great after that.