It tells the engine management computer if the throttle is at idle or full acceleration. So if the switch position is does not reflect what the throttle is doing, your EHA is trying to respond to faulty data. Like it may think you are wide open and go to full enrichment when you are just driving normally.

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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