I did most of that, and still had a rough idle ('89 560 SEL). Took it to a Mercedes only specialist shop that knew well I worked on it, and they showed me a "trick": Very carefully bleed fuel, while at idle, out of all of the eight injector exit ports (one at a time) at the fuel distributor. They showed me how - brown gew cam out, replaced slowly by clean gas. OK, so the idle got a bit smoother. My own "trick" then was to add an in-line fuel filter right before the fuel distributor.

To make the story short - all of this added some MINOR improvements. New injectors, new seals, chasing vacuum leaks, cleaning the idle control valve, all of this, and in the end the idle was still too rough and random.

After years of living with this, I finally recently swapped out all three engine mounts - and the rough idle was gone, FOR GOOD. Smooth - just like a new car. Since this is a relatively easy job, with not too much cost involved in parts, I'd do this FIRST before chasing down phantoms in the engine and throwing money at parts. Interestingly, on this site there were others in the forums that had suggested I look at the mounts when I was trying to chase the source of the rough idle roughly ten years ago. I took your approach on my own back then, but they were right in the end. Lesson learned: I'd start with the mounts first. They are rubber, these cars are old, and they are gone if they have not been replaced.

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)