Always hard to remember the various places such adjustments matter. When you are doing it properly with an exhaust gas analyzer it is apparent. I don't remember.
The knob adjusts in distinct increments (clicks) move it 4-5 one direction...pause... move it back and go the other direction. Go the direction that makes the engine run faster. If it doesn't matter then return to the beginning and leave it alone. There is only about 2-3% CO change from one end to the other if I recall and none of it matters to anything but idle as the circuit is removed when the throttle switch is opened.
Bosch Master, ASE Master, L1
33 years MB technician