I had a similar problem with a 1986 560 SL. My indie shop finally narrowed it down to the EHA valve. Along the way it ate up the spark plugs, oxygen sensor, and left a lot of carbon in the engine and exhaust system. I'm still dealing with that. If it is the fuel distributor, you can add several hundred dollars to the cost of the above parts.
Have it checked out by a good mechanic. Its cheap insurance.
1986 560SEC: 150,000 miles, runs great, but I've got to sell it (too many cars for one man)
1987 560SL: 122,000 miles, used to run poorly, now (thanks to forum), runs great!
1997 GMC Jimmy: Turned out to be a turkey.
1989 T-Bird Super Coupe: 150,000 miles, still runs great. Ford got it right.