Next question: wideband o2 sensor. These cars (and lots of other Japanese cars of the era) have a weird wideband sensor that's sort of like a narrowband, but with different control system behaves as a wideband. Not as good as a Bosch LSU4.9, but still very usable, and without losing any accuracy over a traditional narrowband sensor.
I've attached some papers about this type of sensor.
Here's the key part:
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Apply about 0.4 volts, then measure the current source/sink of the sensor. Current flowing out of sensor, rich. Current flowing in to sensor, lean. Conveniently, the current is linear with respect to phi (reciprocal of lambda), with a different slope on either side of stoichiometric.
Apply voltage, measure current: Hey, that's something I can do with a lab power supply and a multimeter:
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(I know the lab supply shows 0.5 volt, but that's because the internal display is slightly out of cal, it's outputting almost exactly 0.4 volt)
This shows 17uA of current, which corresponds to a very slightly lean mixture.