Have a 2005 Outback 2.5... It has new plugs and wires. 92,000 miles. It accelerates fine and starts fine. When the ac/fan kicks on the computer increases the rpm's but when it drops back down the idle gets too low and rough. It does not stall - yet. But, I am waiting to get that call from the wife that it has stalled. The idle appears to be dropping down more and more the past few weeks and just seems a little more rough with a little vibrating. Any ideas? The dealer finds no codes and seems to think all is OK.

I had a similar problem last summer on MY04 Forester. If your Outback has an EGR, and I'm pretty certain it does, you can read what I documented over on Subaruforester.org:

 

http://www.subaruforester.org/vbulletin/f88/low-idle-stuttering-erratic-jerking-various-rpms-76450/index3.html#post887065