Thanks for the prompt reply.
That makes sense... as simply applying throttle, eliminates the condition. I notice that the tach often jumps more like 500 rpm, up and down, up and down. Curious as to why the manifestgation is so intermittent. It can go all day or more without the sympton, surface for several minutes...in varying degrees of amplitude, and then completely disappear again for several days. Is this a common issue to (a) 500E's (b) W124's (c) Mercedes, or (e) ??

I don't recall the condition ever showing up in the 72 450SEL, 78 450SE, 84 380SE, 84 300TD, 2001 E-55, but I do vaguely recall it in the 86 300E.