I gotta tell ya, this is the first 'low idle' post I've ever read, almost everyone has complained about high idle on the 116/117 engines. There's little to check on the 560SL outside of the IACV, the control box, senders to the control box, and vacuum leaks, and it's a very frustrating exercise. Count your blessings.

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1986 560SL
2002 Toyota Camry
1993 Lexus