I measured this with a dwell meter off pin 1 of the diagnostic socket. It was reading around 25 degrees at idle. The dwell increased as rpm went up. Occasionally it would drop below 20 and the idle relay seemed to start working and brought the idle down. Since the ignition module controls dwell, I replaced it, and the idle speed is where it should be.

My theory is that if the idle relay sees a tach signal above a certain rpm, it quits trying to control the idle.

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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