Your vehicle should have the stored codes in the computer, not only the duty cycle. If the vehicle is a 1992, it should have more diagnostics and codes.
80% duty cycle means a bad intake air temperature sensor or the altitude sensor (they could be one of your problems). But an O2 sensor sounds more like it.
By the way, how is your wiring harness??

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1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
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