I experienced the same problem years back on an 85 380 SE and was able to clean the idle control valve with WD40 to eliminate symptons. Shortly after, I had a valve job done and mentioned the symptoms to my A+ indie. He installed a very small piece of tubing between the two hoses on the ICV sort of like a jumper. A few years later I noticed this jumper was stock on an 87 SEL. Maybe one of resident guru's is up to snuff on this remedy?

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65 190d sold
85 380SE sold
87 560 SL 180K
84 380SE 96K (mint)