bas_500sl, check the condition of the distributor caps, distributor rotors and spark plug wires. If those are in bad shape the engine will run poorly. Bosch replacements would be a good idea ... don't try to save a few bucks on those items. Apply a thin film of dielectric grease on the spark plug wire boots to make future removal easier. Look in the Owner's Manual for the proper spark plugs for your engine ... platinum or newer style spark plugs are a no-no for that vintage engine ... verify the gap is correct, even on brand new spark plugs.

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Fred Hoelzle