Soemone look up this report?
 

Alldata.com for a 1983 240D


58_013 OCT 82 Fuel - Idle Speed Control Test Cable

Leathermang told me about a tech bulletin discussing idle adjustment features MB engineers put in after car was old.

Well,, that was pretty close to what I said... the engineers put something on the injection pump "to be used when the car was old"... in other words, they knew it would not be needed when the car was relatively new... but designed this to be available when it was older and needing it....and it had to do with the idle as far as I remember...