Unplug the O2 sensor and look at its open circuit voltage. It should be over 450mV. Engine and exhaust must be fully warmed up. Also check for continuity of the O2 heater.

I have the following temp sensor values for '84 M102. I'm not sure if they apply to later KE systems, but I think they do.

20C 2.2-2.8 Kohm
80C 290-370 ohm
100C 140-220 ohm.

Take readings at two temps - 20 and 80 are probably easiest.

Duke