What Robert said is pretty spot on...the car will be fine without a tune for a while AS LONG AS you don't push it...if so it may go into limp or even worse lean out an internally haemorrhage. I would change to a Walbro....again a useful safety item. Standard airbox is fine, though saying that mine did gain a reasonable amount with a CAI and silicone intake.
Bottom line is drive it sensibly but get a tune ASAP.

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No Subarus currently owned