Low Idle

[PJH58]

I changed the battery last night in my '05 2.5 SE, and after have a really low idle (approx. 200-300 RPM) that eventually, after warmup, returns to normal. Have i loosened something to cause it or did something not reset properly after reconnection?

[94sportsedan]

After a battery disconnect you should do a idle relearn. After I do a disconnect/reconnect I start the car and let it run till the cooling fans cycle on then off never touching the gas, then shut car down. Now the computer pretty much has a good idea on idle parameters from whatever coolant starting temperature to 204F.

[FrozenNorthLGT]

Haven't experienced this problem with the legacy, but on my 04 dodge stratus I disconnected the battery at around 35k miles to put in an optima for my stereo, and didn't have a problem. 2 years later, around 68k I disconnected it again, to put the stock battery back in before I sold the car, and it wouldn't idle well at all. To make a long story short, apparently a common issue with dodge/chrysler vehicles of recent years is that after disconnecting the battery, they go back to a default IAC setting. If there is carbon built up (and it doesn't take much at all) on the IAC passage, or the throttle plate, the car can't initially compensate, and will idle poorly and frequently stall. After a good cleaning with some carb/throttle body spray, it was good as new. Might be somthing to try, though I dont think I've ever heard of that happening with any subaru vehicles.

[PJH58]

Thank you for your replies. The issue sorted itself out yesterday afternoon, when I let it idle to temperature.

Best of the season to you both!

[WalksBackwards]

I had the opposite problem from the original poster on this. I replaced the battery and the idle when cold was OK but when it warmed up the idle dropped very low so that I had to be quite careful about starting up from a stop to keep it from stalling. I started the engine, put the care in gear and let it warm up to temperature. Put it back in park and shut the engine down. Started it back up and went for a drive with no more problems. Thanks for the post. This is a 2006 Legacy with automatic.