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08 Subaru legacy rough idle when stopping in D or R unless AC is on

K_Rad82K_Rad82 Member Posts: 1
edited July 2021 in Subaru
Purchased 2008 Subaru Legacy for my son. Super nice condition, drove great during test drive. thought this would be a great first car. 118k miles. Drove an hour home, that drive was fine. Started up 3 days later and took for a short drive and ended up stalling out. There was oil places there shouldn't be. Dealer replaced Engine valve cover and spark plugs. Drove much butter but we thought it was still a little off. Cleaned Mass air flow with cleaner. Drove around a bit and then all was good for a few weeks. Until....I took the battery out to fix the airbag light issue that a lot of Subaru's have. Airbag issue is fixed but once I Put battery back in it now idles rough and wants to die. Did Subaru idle re-learn fix video I found online. Now drives fine IF you have the air conditioner ON. If AC is off, it still sputters when you are in D or R and come to a complete stop. My next idea is to clean the throttle body but after that I don't know what to do. Any ideas? I appreciate your thoughts. Trying to avoid a big mechanic bill. Seems it is just something little. No check engine lights or anything. Automatic transmission


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    Subaru_userSubaru_user Member Posts: 3
    If the throttle body does not do it, then what may have happened is your idle speed is too low. Sometimes on the older Subarus the idle setting drops over time. Do you know the RPM when it wants to stall? My guess is that the idle after the engine warms up it drops too low. If you don't have this problem when the engine is cold (as you don't mention this) and the automatic choke is on, it is definitely the idle that needs adjustment. As you said, that is not a major fix and it should be easy for anyone who knows how to adjust the idle to correct in under 15 minutes. Best of luck.
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    Subaru_userSubaru_user Member Posts: 3
    PS - the fact you state it does not do it with the AC is on - the idle goes up to support the AC. That led me to suspect the resting idle at warm is too low.
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    thecardoc3thecardoc3 Member Posts: 5,776
    Have any codes set since you posted this? Do you have a scan tool and can you post the long term and short term fuel trim numbers?
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