After checking oil, fuel (decent stuff) etc, set off in my 1987 230E which had occasionally been misfiring under load, but now seemed good. after a good run of 200 miles with no problems, the missing under load returned occasionally, but otherwise 90+ cruising in a fully loaded car was fine with no ill effects. On slowing from a steady cruise, it cut to 3 cylinders and was nursed home.No noises or nastieness, just running on 3. New plugs were fitted to replace the crusted grey originals, but no difference. Any ideas? fuel injector? Rather stuck now! I have basic mechanics knowledge but wary of going into unknown territory.