Check the condition of the plug wires, cap, and rotor -- these aren't replaced very often on these cars, and second (or third) owners often baulk at the cost for routine replacement. The cap and rotor on my 88TE were terrible -- the contacts in the cap were almost completely eroded off! There was evidence of arcing all over the plug wires, and the plugs didn't look very good, either.
You cannot adjust the ignition timing, it is programed into the computer and calculated off the crank position sensor.
Best bet is to do a complete tuneup, replace all the rubber vacuum hoses, check and adjust the mixture (and check the O2 sensor operation -- if the O2 sensor is bad, you won't get optimum performance). You will probably need to replace the idle control valve hoses, too -- mine were rock hard and leaking.
Change the oil in the rear end, put in synthetic (less drag), change to synthetic tranny fluid and engine oil, check brakes for drag (another place people cheat on maintenance), check for proper tire size and inflation. If the tires are old, they can aquire excessive rolling resistance, slowing your down.
Last, drive carefully, please -- it's nice to have great acceleration, but remember -- speed kills!
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!