Nothing wrong with the mixture setting. It's working as it should. Your miss is either bad injectors, an ignition problem, or a valve problem, it's not the fuel delivery unless you have a bad fuel pump or relay, causing fuel starvation when it stops running or slows down. If it is really intermittant, its very unlikely to be the fuel distributor of the injectors.

Set the mixture to 50% duty cycle and find out why you have a miss, then reset (the miss will cause the lambda control to run it rich).

dirty, clogged, or dripping injectors will cause you to have different mixture in the affected cylinders, so you will get rough running.

Bad plug cables, rotor, cap, or spark box/coil will also cause rough running and mixture fluctuations.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!