I have an '87 560SEL 122K, that will run and idle perfectly for ten minutes or so, then suddenly just appear to load up on fuel. Strong smell of unburnt gasoline, engine stumbling, missing, running on 6 or 7 cylinders. Then just as suddenly correct itself smooth out on the idle, and operate perfectly again. The periods of bad operation were about 30% of the time a week ago, now its 70% bad operation and only 30% good. Whatever is failing is getting rapidly worse as time goes on. Also the idle will vary widely at these times too, sometimes at 500rpm other times 1000rpm. Just tuned up amonth ago so that's not a problem. Any ideas? real frustrating for me, I'm at a loss.