I was going to post about this on my 87 420 but figured maybe it was just me. I don't really feel it on the highway but when letting off the gas around 40-50mph, I can actually see the tach needle cycle up and down a few millimeters slowly as I coast. I'll have my mechanic look at the throttle idle contact.

John

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04 C230K Sedan
01 Boxster

00 C230K Sedan (sold)
87 420SEL "Phatryd" (sold)