Hello rickyd,

Is your problem intermittent? If so, these problems can be hard to diagnose and expensive to repair.

If it happens every time a good MB mechanic should be able to diagnose and repair it but in some cases the testing of a component can cost as much as it’s replacement (if you do it yourself and scrounge for parts).

Check to see if the ICU is loose. It is on the driver’s side fender behind the headlight area and has a wire that goes to the coil. Mine was loose and hot. My friend has a 1985 500SEL and his was loose as well. Both his and mine had only 2 of the 3 mounting holes with clips and bolts. Actually, I borrowed his for a few days to confirm that my ICU was bad.

My 500SL still runs rough below 2000 RPM but at over 100,000 miles it could probably use fuel injectors and plug wires. I want to change them to improve the idle (and exercise my limited mechanical ability). But I think I will have it put on a scope first. I have heard from more than one source that these motors do not idle well but I think they just need to be well maintained.

Let me know if I can help.

Steve
1985 500SL Euro

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Steve
1985 Mercedes 500SL Euro (Gray market)
1995 BMW 520i Euro (Gray market)
1992 BMW 525it Wagon
1994 Honda Del Sol Si