http://www.landiss.com/mixture.htm
see 25-27 here: http://www.w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/103/07.3-1100.pdf

Adjust at operating temperature. Need a long hex drive 3mm I believe.

Disconnect and cover regeneration valve with electrical tape. Leave air cleaner in place. Use hole in air cleaner to adjust. Use very small adjustments (1/8 turn is a lot). (Removed air cleaner or not covered regeneration valve would be same as vacuum leak and you are setting air/fuel mixture and would also be about 9-10% off.)

Place multimeter red in pin 2, and black in pin 3 of X11 for Mercedes duty cycle calculation. Set mixture adjustment to average 47% duty cycle at idle. Look at duty cycle at 2500 rpm's and see if it is within 10 points. The reading should fluctuate somewhat rapidly as this is in response to the O2/lambda sensor relaying good info. If no duty cycle reading on your meter the math calculation is in first link above.

It should be smooth running at idle and responsive just off idle and within 10 points at idle and 2500 rpm.

You can adjust for your best performance but just keep it within the 10 points. Counter clockwise adjustments are lean. Keep up with where you begin and all adjustments made so you can put it back exactly where you started if you decide to.