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Old 06-05-2007, 10:43 AM   #1
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Rough Idle with AC on

2002 Focus, Auto Tranny

I had the alternator replaced last week. Now I get a very rough idle (stumble) with the AC on when stopping at traffic lights. Tach seems to bounce between 700 and 100 until I turn off the AC. Idle returns to normal once AC is off.

If I turn on the AC while stopped this does not happen. Only happens when slowing down.

Is there a sensor or electrical connection that controls the idle that may have been affected by the partial car disassembly involved with an alternator replacement?

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Old 06-05-2007, 11:33 AM   #2
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when they disconnected the battery to install the new alternator it reset the computer's idling, just disconnect the battery put the parking brake on reconnect the battery and start the car, let it run for a minute, then turn on a/c lights radio and let it sit another minute, then drive for about 30 mins so the car can relearn its idle!!
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