My '83 380 sel was running perfectly until a few days ago. Now it won't idle. When I stop for lights the idle drops then the engine stalls. It has also started running very rich. Black smoke out the tail pipe, sooty black plugs (near new Bosch supers), and very poor gas milage.

I changed the idle control valve and idle control unit with a known good set, but it made no difference.

Where should look next. Thanks.

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2000 Mercedes S500
1990 Mercedes 560SEL
1970 Triumph Spitfire