As I mentioned in my original post, the idle drops if I unplug the ELR. But the linkage might be related to why it starts at 750 and then sticks at 900 once the pedal has been pressed.
With the ELR disconnected, engine starts at 500 rpm and sticks at 600-700 if I rev it. Idle is also very rough without the ELR.

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1985 190D 2.2L 717.411 5-speed
1983 300D Euro OM617.950