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

I would check all of the vacuum lines next. Bend each rubber connector - if you see cracks, replace it. The plastic tubing used, is probably quite brittle by now...be careful.

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D

The idle valve has no part in mixture control!

Mixture control is monitored on your car by watching the duty cycle of the frequency valve. Pin #3 of the diagnostic socket.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Warm up regulator. A CIS fuel pressure guage is needed to diagnose. If it is bad, call Phil at the Buy Parts section of this web site. There is a programable replacement available.
Paul

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84 500 SEL (307,xxx miles)

A new O2 sensor and a fast run to blow the carbon off the plugs and it runs and idles perfectly.

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2000 Mercedes S500
1990 Mercedes 560SEL
1970 Triumph Spitfire