I don't have an answer for Randall, but I have a related question:
Why don't later-model M-B diesels have an idle adjustment control
on the dash like the 220D did?

Or if you prefer, why did the 220D have one?  The only other modern
cars I'm aware of that had this rather odd feature were the early
rotary Mazdas, e.g., the RX-2.

Geoff

--
"America is the greatest, freest and most decent society in
existence.  It is an oasis of goodness in a desert of cynicism
and barbarism. This country, once an experiment unique in the
world, is now the last best hope for the world." -- Dinesh D'Souza

Look between the injection pump and the block where the "idle stop
screw" is located (it points up at you). It has a lock nut that can be
loosened with a 5/8" deep socket. Then use a large and long flat blade
screw driver to unscrew the adjustment. Try one 360 degree turn and lock
it. Drive it a a few days and adjust again if needed but keep a record
of adjustments made so you can retrace if necessary.

While it may seem too fast at hot idle the motor also has to idle
reasonably at cold start so test it through the full range of driving.

As to the other poster's question, the later engines have a 750 rpm idle
speed governor inside their injection pumps making a hand adjustment moot.