I'm not too familiar with the M112, my E320 has an M104. However, I experienced similar problems on my car a while back and it was caused by a bad MAF / AMM. Does yours use hot film? Those are the more problem-prone ones. A new one on Fastlane is about $250 for my car. If yours is due, it might be worth a shot exchanging it.

I believe misfiring caused by the plugs would trigger a CEL. Same thing if caused by the EGR. In my experience, MAF / AMM can be just on the edge of performing and can produce drivability issues without triggering a CEL.

As a test, see if the car performs OK when you acclerate VERY VERY gradually. My car would accelerate fine doing so, and also if I nailed it. However, if I drove it like a normal sane person it would have a pronounced flat spot and/or would buck or misfire. This behavior was very pronounced in the winter when cold (probably because the MAF also measures intake air temp). When warm, it started fine but would idle very rough if left to sit for about an hour and then restarted.

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86 W126 560SEL
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79 W123 250
78 W123 280E
75 W114 280