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For 'adjusting' the Oxygen sensor output waveform it may be satisfactory to use an op amp configured as a unity gain non-inverting dc amplifier with provision to slightly vary the dc offset of the output waveshape. It seems that the normal sensor signal doesn't vary in amplitude, but rather, varies in response to 'richness' by increasing or decreasing the magnitude of positive dc offset.
This is easily accomplished with an op amp circuit.