Originally Posted by ArtD

First off, hi everybody! I have a 1989 560SL with just over 80,000 original miles. I am the third owner and have owned the old girl for about 2 years now. The previous owner's very good Mercedes Mechanic had done a pretty decent job of maintenance.and all of the filters were brand new when she got passed along to me. I have put about 12,000 miles on, this was a very low mileage car.

About a month ago I notices signs of what appears to be vacuum building up in the tank, with an accompanying "wooosh" when the cap is removed. Then yesterday a couple of miles from the house, all of a sudden very rough running ensued. like 4 cyls dropped, just like that. Made it home. this morning, starts fine, idles good, revs up fine when not under load. I forgot to mention that when cold, seems to be running rich. I have done some searches for certain things, but of course, every problem has its own set of circumstances. Does the tank suck relate to the sudden loss of power? I have done nothing yet as far as diagnosing anything. I'll start with a plug check, etc. I should mention that I am a pretty fair mechanic with a good set of tools. I have a complete set of 560sl manuals, as well as a Bosch fuel injection book. This could well be an electrical problem, like a bad coil. All the rest of the ignition parts are quite new. Before I tear into things, I just want to get a feel for possible avenues to pursue. Thanks guys!!