No good man. The MKIII only has a narrowband O2 sensor... it's about as useful as having some junkie sit with his nose in the exhaust and just yell is he's getting high or not.
A narrow band sensor only tells the ECU if it's on target, rich or lean... but not how much. It is basically a three position switch who's center position (optimum; ~.6v) indicates only 14.6:1 to 14.8:1.
A wide band provides information on the mixture from around 10:1 up to 21:1...
Ideal mixtures for gasoline engines start at around 13.1:1. You'll want between 10:1 and 12:1 depending on how much boost you're running, intake temps and so on.... 10:1 is safest but you lose mileage and a little power.
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