[SoCal LS-L]

Mines doing the same thing, and every once in a while it will stall, but just when its between cold and normal temp and I put in park. I have gone through it thoroughly, and have it narrowed down to the Idle control under the throttle body. This requires removal of the intake manifold, and it also will allow you to clean the other valves and solenoids under there, as well as replace the vacuum hoses and PCV valve. While the intake manifold is off I would strongly recommend cleaning out the EGR passage and the main air chambers. The needed gaskets are available at subaruparts.com ( 2 intake manifold gaskets, throttle body gasket, EGR line gasket ).

Your situation might be different, theres a number of reasons for a low idle, the easiest thing to try would be to adjust your TPS. I suspect your Idle air control valve may be clogged, as its pretty common as subaru engines seem to ingest a lot of crap from the PCV system.