I would suspect lean running after warm-up. Best course of action is to get the hot mixture checked with a CO meter, but failing access, you could try the following:
Make SURE you don't have a vac leak somewhere (or that you have not recently fixed one!). If you find any, fix them.
Make sure the ignition is up to snuff -- that means good cap, rotor, wires, plugs, and points. If the ignition is weak, it will run poorly at the correct mixture because the spark is weak.
Check the tailpipe -- if it is black and sooty, expect an ignition prolbem.
lastly, and only if you cannot find anything else, pull the cover on the ECU and turn the adjustment wheel a couple clicks clockwise. This will cause it run run a bit richer. If there is no change, turn back to the orignial setting and llok for the vac leak. Remember, the intake manifold is in two parts with seals (8 of them) between, and there are two seals on each injector, too! Bad door locks or climate controls can also give you a vac leak, so can the large hose to the MAP.
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!