Ford Focus Forum, Ford Focus ST Forum - View Single Post - Engine starts to idle rough when brake pedal is pressed
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Old 12-07-2012, 11:58 AM   #2
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Brake light wiring shorting to ground, putting a increased electrical load on the alternator, which drags down the motor.

The IAC should compensate with idle speed increase to prevent dying, if it runs rough at 800 rpm, the IAC can't fix that.

(just a wild arse guess)
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