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Old 12-17-2006, 11:15 AM   #1
GearDriven
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Rough Idle -- Bad Battery?

So my 2005 Focus was in an accident. It sat on a lot and the battery discharged. They got it charged and it started right up after 10 days sitting. It's been having a rough idle ever since. The cause appears to be a slow idle. The battery may be on its way out, as I am also getting a low voltage DTC. Any ideas? The dealers are all backed up around here.


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Old 12-17-2006, 12:22 PM   #2
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I'd take it to Autozone or PartsAmerica or whatever you have in NY, and get a free code read done. They can also put a meter on the battery and see if you're putting out the right voltages at idle and at higher RPM.

If the battery fully discharged sitting on the lot, the computer needs to learn all the idle parameters again. This is accomplished on first startup after the battery is reconnected, and is described in your owner's manual. The repair folks may not have done this properly, and the car's idle will suck until the car slowly figures everything out. You can disconnect the battery, wait awhile, and reconnect it, then follow the relearning procedure properly and see if that helps the idle.
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Old 12-17-2006, 01:23 PM   #3
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A battery would not make your car have a rough idle. If you have a worn battery your car would have 3 effects. They include not starting obviously, lights dimmed while driving, or a hesitation when starting the car (the car woul take a few cranks to turn over). If you have a rough idle I would check the following items first; Spark plugs to see if they are fouled, ignition wires, and even check the air filter).
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Old 12-18-2006, 11:56 AM   #4
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My thought is that maybe one of my plugs is fouled/not gapped right and it's not related. OR: the prior owner removed the resonator or did some other internal mod to the stock intake and the ECU was "reset" by the battery death and hasn't "relearned" what was wrong before.
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Old 12-18-2006, 12:11 PM   #5
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Dead battery= reset ECU, your computer has to re-learn it's map, especially the idle map. If you don't do it how the manual describes it will take about 2 weeks, and then suddenly one day- poof, clean idle. That's how long it took mine before I knew to allow it to sit for 5 mins idling.
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