Try pulling the connector off the valve just enough to get your test leads on the pins and measure the voltage. Start the engine and let it idle. That way you can see what the idle relay is sending to the valve. I don't have the manual in front of me, but I think you should see 4 - 6 V.

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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