Per Steve Brotherton, if the voltage from the air sensor potentiometer at idle is out of spec, the ECU will not understand that the car is at idle and thus decide to go into a sort of limp mode, cutting the power to the idle valve and retarding the timing.

The spec is .5-1.2V output at idle measured across pins 1 and 2 at the pot. The easiest way to measure is to remove the back of the connector. I tested at the pot and found .07V. Adjusted it up to .8V by rotating the pot very slightly, maybe .1 mm. Now have perfect idle including AC compressor signal - no more drop when the AC comes on.

I tested the Key On values at the ECU harness, but did not test at idle because of the good readings from the EHA current. Lesson learned.

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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