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Old 09-11-2010, 06:30 PM   #1
Scooby Newbie
Member#: 136402
Join Date: Jan 2007
Default After New Battery Idle Speed Goes Very Low

So my dad's 06 impreza wagon has been having problem such that it runs fine but every morning he'll need a jump to get it started. I measured the voltage and got the following results:
off: 12.9 v
idle: 12.5 v
2000 RPM: 13.9 v

Therefore, I draw the conclusion it's the battery that needs to be replaced. However, after i got a brand new deka ultimate group 35 battery and installed it, the idle suddenly goes to almost nothing. The car starts w/ trouble but it'll start. I suspected the battery and brought it back to the store and they showed me everything is w/ a battery meter. And what puzzles me more is I put his old battery back on and now it also has the exact same very low idle (near 0 and car shakes) speed problem.

any idea? did I accidentally screw up something? did I need to reset something? please help. thanks.
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Old 09-12-2010, 02:43 PM   #2
Scooby Newbie
Member#: 225057
Join Date: Sep 2009
Chapter/Region: SCIC
WR Blue


I believe this is a normal issue whenever you replace a battery on a newer vehicle nowadays. Same thing happened to me when I replaced the batt on my wife's camry. The ECU needs time to re-learn the engine settings when it is reset and it will eventually resolve itself after a few minutes/miles of driving. I just drove it around the block a few times and now everything is fine. Darn cars are too smart for there own good!
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Old 09-12-2010, 04:18 PM   #3
Henry H
Scooby Newbie
Member#: 184330
Join Date: Jul 2008
Location: Southern California
2008 Impreza 2.5i
Dark Grey Metallic


^^^^^^yup, what he said.

If all you did was replace the battery then it might just be that the ECU is re-learning. The ECU has been resetted so just give a drive for a bit and see ir the problem continues.

I'd say go for at least 100 miles of normal driving.

Just make sure your air filter has been maintained recently just so your ECU doesn't have to compensate for a dirty filter. Maybe even clean your air flow sensor with MAF cleaner.
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