Engine rocks back and forth at idle
 

I replaced the engine mounts on my W124 before memorial day weekend (what a difference!) and although I don't have any vibration, I now have a slight engine rock at idle which can be seen with the hood open or felt inside the cab (similar to the W123 rack damper bolt issue, but the W124s don't have those, IIRC). It was probably there before, but the other vibrations were so offensive it was not as noticeable.

Has anyone experienced this, and what was the resolution?

Haven't had this problem, but did you change the transmission mount? I like to do all of them together.

My injectors were recently cleaned and balanced by Greazzer, that fixed all engine motion at idle for me. You have to put you hand on it to feel it moving.

Another possibility: rebuild the delivery valves.