This refers to the throttle vakves of the M70 engine, E32 750, E31 850. For a smooth idlethe most important point is the area between wipers and contact material, see page 3
wear of resistance material is the point.
But you can measure them

I got the Bosch data translated for checking the values of the DK's

open the file there called: DK input details : small PDF file

Of course, the throttling valve should be completely disassembled and cleaned about every 60 k miles in my opinion, checking for dirt, checking the 2brushes from the DK motor etc.

Download those data , do not hotlink them, thanks