I asked the shop about the idle valve. They said that they tried another one, but it made no difference.

You raise a good point. I assumed that on this model, with no power the valve was closed and that's the way it was designed. I will look into this some more.

[Added 9/9: per Bob Terry and David Poole, and the MB documentation, with no power, the valve is closed]

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe