Found a table listing resistance for Bosch 0280130032, tested two old sensors, '84 and an '88. They both failed on the high side and the low side. Resistance at 80C, according to specs, 290-364 ohm.
The '84, 590 ohms, the '88, 700 ohms. Cranked the temp to 90C and 480, 540, respectively. Used digital thermometer and water, repeated.
They should have registered 300, better if 290 ohms at 80C. So, unless I'm a ham fisted lunatic, I think I need a new unit.
End of tailpipe was always black, plugs tan only on electrode and ground projection. FWIW, another afternoon ticking away. Cheers bricksters