Air flow meter im guessing. got the same car as you, happen to me a few months back, wen it comes on boost, it feels like it hesitating to go and it idles pretty rough, sometimes stalks from a rolling stop. Got a brand new AFM from Subaru, chucked it in(if u have the right tools) let it idle for 5mins or so. It was back to normal
![Wink](images/smilies/wink.gif)
good luck!
![Smile](./images/smilies/smile.gif)
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