2005 2.5i rough idle - Subaru Outback - Subaru Outback Forums
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post #1 of 17 (permalink) Old 06-07-2010, 11:26 PM Thread Starter
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2005 2.5i rough idle

Hoping that SOMEONE has maybe figured this out. I know I'm not the only one.

Battery died 3 days ago. Immediately following replacement, idle was very low and rough, primarily when in gear but also occasionally in P or N. Drove for about 8 cycles (hoping it would heal itself as it usually does), and finally got CEL and flashing cruise. Code P0506, low idle. Checked for obvious vacuum leaks/disconnected hoses and squirted brake cleaner at connections I could see. No visible or audible leaks and no change in idle speed with brake cleaner (but how do you know if you found all the connections?). Pulled the tubing off the driver's side of the air box, and only a slight drop in idle speed. Replaced air filter (stock). Today it began doing a bump (maybe a rough downshift into 1st) when rolling to a stop. Also a fairly strong surge every now and then when it figures out it's idling too low. It's summer here so the AC is always on, but the surge does not always seem to coincide with the compressor engaging. It might be my imagination, but it seems to act up only when moving. It will idle OK in the garage, even when I turn the AC on and off and put it in and out of gear (it seems to adjust to the added loads). But, as soon as I back out about 20 feet, the idle drops and becomes erratic.

I've read varying things about cleaning the MAF sensor; seems like most threads indicate it didn't permanently fix anything. It's a little furry, so I'll give it a try when I can get some proper cleaner.

New to the site and new to thread posting in general, so thanks for any help.
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post #2 of 17 (permalink) Old 06-07-2010, 11:38 PM
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Take the throttle body off the engine and clean it thoruoghly with a clean rag. Check plugs also. Sadly the throttle is not adjustable manually its all computers and gizmos.
I would look for a vacuum leak if you are getting codes about low idle.

Yeah, mine shakes at idle, they all do that..........right?
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post #3 of 17 (permalink) Old 06-08-2010, 08:01 AM
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Was the car running fine immediately before the battery failed -- no rough idle, etc etc? If so, then I would tend to doubt some sudden change in other areas, such as the throttle. (The exception being areas that were, or had to be, disturbed when the battery was changed.)

Check the new battery charge. Was it fully charged up before it was installed, or was it just quick-charged or straight-off-the-store-shelf? Weak batteries often cause malfunctions in the electronics. Also, with the AC on all the time, the alternator might not be able to charge up a battery that was initially only partially charged.

It's not unusual for a glitch to develop in the ECM software when it loses power (totally, as when the battery is disconnected) or when being reconnected. This is often resolved by disconnecting the battery, waiting a few minutes for residual energy to be drained from the electronic circuits, and reconnecting. Worth trying before diving in to other areas.
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post #4 of 17 (permalink) Old 06-09-2010, 07:57 AM
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Besides cleaning the MAF and the other suggestions, IAC valve dirty maybe ?

If it was fine before and a battery failure started this, like plain om said, check the voltage on the battery ... they rarely come fully charged and depending on the driving distance can take a very long time to charge up fully with the alternator.

A disconnect the battery "reset" is usually my first attempt at solving electronic issues. While it's disconnected, press the brake pedal to speed up voltage discharge and, check all the fuses, you never know what's gonna happen when a battery dies.
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post #5 of 17 (permalink) Old 06-19-2010, 01:18 AM Thread Starter
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Rough Idle Solved

Plain OM wins the sweepstakes! Not having time to throw a charger on it, I just toughed it out without AC for about 30 minutes at freeway speed, and it must have charged enough, because all has been well ever since.

Thanks!!!
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post #6 of 17 (permalink) Old 06-19-2010, 05:22 AM
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You should still find the time to throw that battery on a charger.

30 minutes on a charger at 6 amps would have probably charged it all the way up ;]
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post #7 of 17 (permalink) Old 06-19-2010, 10:03 AM
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Same happened to me after a new battery. apparently the computer "forgets" how to idle properly...leave the car idling in your driveway for 30 minutes and it re learns what to do. Worked perfectly in my case.

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post #8 of 17 (permalink) Old 09-06-2011, 08:31 PM
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I had the same problem – battery dies, replaced battery, car idles low and stalls out. I ended up taking it to the dealer. On the service ticket, it said “performed ignition timing learning procedure. If you want to DIY it, here’s what I was able to find out:
  • Disconnect the negative battery lead
  • Press brake pedal to drain residual voltage (verify w/ DMM). Or, wait ten minutes.
  • Reconnect neg lead, make sure both battery terminals are tight.
  • Insert key, rotate to ignition position (you should see gauges sweep)
  • Wait ten seconds, to allow "throttle initialization".
  • The loss in power is from the ECU ignition timing learning being reset. DAM/IAM (Dynamic/Ignition Advance Multiplier). To accelerate this learning period, bring the car to operating temps and do a few quick 3rd gear burst maintaining 50-75% throttle. This will bring the ignition timing back up and have your car back to normal.
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post #9 of 17 (permalink) Old 11-06-2011, 11:18 AM
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I've had my battery out a couple times and every time I replace the battery, the car idles rough or stalls. Soon thereafter, it will seem to fix itself. Usually happens after driving around and letting it idle here and there. I don't understand why, but it seems to fix itself. I have a 2005 Outback 2.5i.
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post #10 of 17 (permalink) Old 12-21-2011, 04:06 PM
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I am having a similar problem with my 05 Outback. I had a CEL (P2098) that I reset with my diag tool. After that, it seems that my car doesn't want to idle any more. When I come to a stop, it will drop down below 500 rpm, and feels like it will stall. It has not stalled at this point yet. In looking over other threads, I think that resetting the code may have something to do with the problem. Does anyone know if that is true... does resetting a code cause loss of learned idle settings on these cars?
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