I agree with Benzmac. Have the distributor head done at a shop because as he said especially concerning lambda adjustment. If you have a meter, then fine, but I'd have it done by someone who's done it before. If you do decide to jump into it yourself, you can e-mail me for the specifics. Oh, you might also want to try the Red Line fuel cleaner product. I have only seen it on their website, and don't have any past experience with it but I can say their other products are wonderful. Check PartsShop to see if they have it.
'67 250SE Cabriolet
'93 300E 2.8