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There are cases where a resulting lambda/AFR value oscillates back and forth with a too high amplitude. Normally, it moves between lambda 1.03 and 0.97, but if it goes beyond, for example, 1.05, you can notice such amplitude oscillations (around 1 Hz) as a “feels like pulling” effect.
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What would typically cause this?
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Unplugging the connector and running everything permanently in open-loop mode fixes the symptoms — but not the cause. And those who managed to get everything working again wouldn’t want to give up the regulation anymore.
Fun fact: I don’t know of a single test report from the years 1980–1983 that claimed the reputation of the Porsche and BOSCH engineers was ruined because the U.S. models with the K-Jetronic from those years had issues.
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At this point I do not want to just leave the O2 senor disconnected. That's why I am trying to understand what could be causing this issue.
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Yes, connection seems done in a poor way.
Regarding the Porsche part suggestion, ... a genuine BOSCH sensor, or a good-quality alternative from another manufacturer, will work just as well — it simply needs to match the BOSCH part number 0 258 986 501.
However, when using a narrowband sensor, I strongly recommend switching to a 3-wire version with an integrated heater (BOSCH part number 0 258 986 502). Connect the black wire to the lambda connector, and the two white wires from the heater: one goes to ground (GND) and the other to switched 12 V — ideally via a relay controlled by the same signal as the WUR. This way, 12 V is only supplied when the engine is running.
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This is the connection that Bosch provided with the replacement O2 sensor. From what I am seeing 0 258 986 502 and Bosch 11027 are the same sensor. Can anyone confirm that? I have 11027 installed currently. I do like the idea of a 3 wire sensor with built in heater.
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The rule of thumb is:
When a lambda-controlled K-Jet system is working properly, it delivers performance throughout the entire RPM range without any surging or similar. I can confirm this from my own experience and from others who have finally set up their systems correctly and, where necessary, replaced faulty components such as sensors, ECUs, switches, plugs, or wiring.
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What would be the signs of a failing ECU? I have opened mine (0 280 800 055) and visually nothing looks burnt or failed but I have not yet sent it out to be bench tested.