First, I would look at the spark plugs. Next, check for corrosion on the resistor-ends of the spark plug cables, distributor cap and rotor. Then look into fuel and air filters. Finally, maybe, run some additives in the fuel. Beyond that, it is time to take it to the technician, unless you have the manuals on CD, digital multimeter, hand-held vacuum tester, time, etc. Cheers, Andrew Seidel.
85 500SEC Lorinser
83 300D Turbo