My test was to hook up a model train transformer to the valve and see if I could vary the idle speed by varying the voltage in the 3 - 6 volt range. I found that it took almost 8 volts to get the idle down to 600 RPM or so, and the spec is 4 - 5 volts.

So I replaced the valve, which improved matters somewhat but I think the control unit is fried as well. I am looking for a used one to come up.

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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