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Matt
Matt, Engineer
Category: Mercedes
Satisfied Customers: 20588
Experience:  Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing
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Have a 1985 Mercedes 500 SEL. Starts fine but will idle down

Customer Question

Have a 1985 Mercedes 500 SEL. Starts fine but will idle down in a minute or so running rough with black smoke coming out tailpipe. Have to hold down accelerator down to idle about 1500 RPM for about a minute or so until the engine idles fine. This happens after each shutdown
Submitted: 1 year ago.
Category: Mercedes
Expert:  Matt replied 1 year ago.

Hello

I'd say this sounds like the warm up regulator is sticking ( item 8 in the image)

as its the mechanical fuel injection system K-jet on these

I'd suggest that the regulator needs stripping down and cleaning to ensure it moves freely

if its badly corroded it may need replacing