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2011 Outback 3.6R Limited
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30 Posts
Discussion Starter #1
Whenever the outside temp is below around 45-50 degrees, my car runs rough in gear at a stop, but it's smooth as butter when it's warmer outside. Problem is mostly solved when I put it in neutral and gets a lot better when I put on AC, but I've concluded that's just because it raises the idle a bit. The problem completely goes away when I get moving; It's a very smooth running vehicle whenever I'm not stopped! Idles rough whether the engine itself is cold or completely up to temperature (around 200). The odo is at 136k, with all the proper services being performed at 120k (spark plugs, etc.). I do oil+filter changes with high mileage synthetic every 5k miles. Fuel trim values are within proper range at idle. I have cleaned the throttle body, changed my air filter, and cleaned my MAF sensor. Done an inspection of all vacuum lines, no hissing coming from the engine bay.

I noticed the problem when it started getting colder here this October. It ran buttery smooth all summer, and continues to run great whenever the temperature has been above 50 here. I've realized this since we've had quite a few warmer days over the holiday season. I've asked quite a few people but haven't gotten any answers. If anyone has any suggestions, please let me know! I previously posted about my rough idle concern thinking it was related to AC, but I have been able to confirm that it is related to the temperature and hope that someone here has some thoughts about the situation.
 

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2011 Outback 3.6R Limited
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30 Posts
Discussion Starter #2
Also want to clarify that I do not have a check engine light or any stored codes.
 

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2010 Outback 3.6R 2014 Legacy 2.5i 2003 Legacy L special edition (retired to backup)
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1,489 Posts
first thing I would do is check that everything is tight on in intake tract (no loose clamps)
 

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2011 Outback 3.6R
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55 Posts
Did you ever get this resolved? My 2011 has the same behaviour, and I have done the same fixes you have. I am looking at transmission/engine mounts now.
 

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2011 Outback 3.6R Limited
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30 Posts
Discussion Starter #5
Did you ever get this resolved? My 2011 has the same behaviour, and I have done the same fixes you have. I am looking at transmission/engine mounts now.
For me an old trans mount was the culprit. One way to tell if that's it is if your vibrations are mostly in the steering wheel due to the mount's proximity to the steering rack. Otherwise I would check your motor mounts. The rubber tends to harden up when it's cold so it will transfer more vibrations. My issue didn't really get much better when the engine actually warmed up, it was mostly just a lot worse when ambient temperature was low no matter how hot the engine was.

If your car runs rough when cold but gets smooth when the engine warms up and you've already thoroughly cleaned your MAF sensor (which also contains IAT sensor), I would hook up a scan tool and check to see if your coolant temp sensor and IAT sensor are giving good values to your car's ECU. Coolant temp in the morning should be somewhat similar to ambient temperature, same with the intake temperature. And then going from there your intake temperature should be hotter than ambient as the engine heats up. Normal coolant temperature range when warmed up for the 3.6 is usually around 195°F - 205°F.
 

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2012 Outback 2.5 Limited
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948 Posts
Yeah you can bench test the resistance readings from the IAT sensor (part of the MAF assembly) to make sure the temp reading is correct:

Using an ohmmeter/multi-meter measure pins 1 and 2 (1 is far right) on the MAF unit:

-20C/-4F should give a 16.0 +/- 2.4 kohm reading
20C/68F should give a 2.45 +/- 0.24 kohm reading
60C/140F should give a 0.58 +/- 0.087 kohm reading

I think you can plot out a graph based on those three points - they're the only points the FSM provides. To achieve the lower temp readings you can put your MAF in the freezer for a while.
 
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