if you have no joy after cleaning the afm.....

also try cleaning the idle stabilizer valve (its the small cylinderical thing on the throttle body held in by 2 phillips head screws and has one big plug) i found my plug was susceptible to moisture from my tmic waterspray but once i uplugged it, sprayed some contact cleaner in there it worked alot better and didn't seem to 'hunt' anymore

i personally think this is a fuckup on behalf of subaru to put something like this plug so close to the bonnet scoop where water can easily get in there, i quite often see that water calcification (white shit) on that plug

oh yeah & clean the inside of the ISV with carby cleaner or upper engine cleaner as it can get a bit oily gunky from oil blow-by in the intake if you don't have a catch can

worth a try before shelling out for a new afm