Thanks for the info!
I had replaced my caps/rotors last year and like you, no help.
I am starting to think you're right, that it's inherent in the breed. I bought my 400E when it was a young pup, 3 years old and 25,000 miles, coming off someone else's lease. I remember taking it in right after I bought it, and complaining of this very same idle. "That's just the way the V8s are" was the response. At the time I thought it was hogwash, since I figured the more cylinders, the smoother the idle.
I have no other engine-related problems -- mileage is good (20/25), starts quickly in all weather, good acceleration -- so yep, maybe "They all do that". . .
I will be VERY interested in your timing chain experiences. I am really torn about what to do. I surely don't want to spend thousands of $ for damage related to chain breakage, but my tech says "Leave it alone until it gets noisy" and so does Stu Ritter, who owns a 400E. I hear there's a lot of labor involved to get to it and the rails.