This weekend my mother was driving a long distance in her '86 Mercedes
450SEL and it started to run rough. When she pulled over there was a
tiny bit of smoke wafting from under the air filter which sits on top
of the engine. The smoke stopped once the car cooled down, but the
engine still shakes and idles more roughly than it used to. There is
a noticeable clicking/ticking noise than gets louder and faster as the
car approaches 2k rpm. There is a slight hesitation in acceleration.
The oil pressure and temperature are consistent and normal. There are
194k on the original engine.