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The vacuum leak would show the car as running lean. Because air is coming in after the Mass air flow registers it there now is more air than fuel. The computer would pick this up with the oxygen sensor and it would show a bad oxygen sensor.
I suggest you taking it to the dealer and fixing the leak. I don't know where it's leaking from so it's hard to give you a ball park figure. However it could be as simple as a hose and it could be a intake manifold gasket so price range $100 - $400 is your ball park figure.