I also have a (sporatic) rough idle. It usually starts 15-30 seconds after coming to a stop and only when the engine is at operating temperature. In fact after a cold start you can feel the roughness start as the engine comes to operating temp. I'm thinking its a non-electrical problem (ie:vacuum or fuel). At this point I'm taking BENZ300's advise.

Mark
1989 300se
69,000 mi