Well, if you keep replacing things, sooner or later you'll get around to the carburetor. If it's intermittent (comes and goes), then it's not your suspension. Black deposits on plugs = running rich. If it was consistently lean but occasionally rich, then the plugs would tell you a different story. Get the carb repaired or replaced. Could be main float, metering rod internal vacuum leak even a cracked fuel bowl. 4 cyl engines are not famous for being smooth anyway. If there is a problem with fuel, they can really rock and roll.
1987 BMW 325
[This message has been edited by jeffsr (edited 06-19-2000).]