UPDATE: New coil solved the problem. Installed coil, cleared codes, and drove - nice and smooth again. So it seems that a bad coil can indeed trigger a fault code on just 1 cylinder, even though it fires for 2 cylinders. Thanks everyone.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280