The idle controller is easy to check. Pull the connectors to the valve back enough to get the pins of your meter on the connectors. You should see 3-4.5 DC volts.

On an 81, you can also pull the connector off the temp sensor at the right rear of the engine and bridge the contacts (warm engine). You should see an increase in RPM's to like 900 because the idle controller thinks the engine is cold. This will tell you if the controller's little brain is alive.

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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