I measured the temp sensor at pin 21 on the CIS connector. The resistance goes down as expected and resistance is to specification as engine warms up. That is not the problem. Car always runs open loop.

Next I started the car with the CIS disconnected and car started and ran the same as when connected! Also the MIL simply times out after 3 seconds with KOEO whether or not the CIS is connected! So that is not proof of a good ECU. With the CIS connected i disconnected the O2 sensor and ran the car, and no MIL!

car remains in open loop at all engine speeds including 2000rpm.

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1972 450SL
1982 300D Turbo