I recently had this problem on my 07 wrx (p2443: secondary air pump shut closed). I considered all the solutions, but since I'm in California and my smog check is due pretty soon, I went with just replacing the faulty valve. I went to a reputable Subie mechanic here in socal and was charged 350 for the part and it took less than two hours for the repair. I've driven the car about 250+ miles since and have no problems yet.