So bottom line is: even at idle the air flow valve should be slightly open, right? (what is sligtly? - a couple of mm?)

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1983 560SL Megasquirted (originally 380SL)

My former Mercedes:
1985 300SD ~190k
1990 560SEL
2000 C220 CDI
1983 380SEC 102k dual-chain conversion
2000 C280 70k (sold)
1987 300DT (W124 - sold)
1972 220D (sold)
1971 220D (sold)