'Miss' in engine at idle when hot... sometimes
 

My 560SL with low miles has been idling roughly sometimes, but not always, after it gets up to running temperature. It seems to have a 'miss' in it.

Any ideas on what is causing this?

MY 560SEL was doing the same thing. It was an open plug wire. A good wire should read about 2k ohms. A new set of BERU wires and NGK plugs cured the trouble. It takes more power to fire a plug at higher cylinder temps.Make sure you are not using resistor plugs.

Two other possibilities is a valve issue, which can be verified by a compression test, or a dirty injector which can be cleaned.

Tom W

Also check for vacuum leaks. It's a common problem in the old engines.