You will need to get the ecu reset by someone with the necessary electronics. The car will run normally, it's just the ecu thinking there is something wrong (whatever was unplugged, now no longer works in the eyes of the cars computer brain).
Induction kits can be pretty good, but can also be a bit of a pain. Make sure the fuel mix is still correct, it could run lean. Also, when the under bonnet temps get hot, it may mean the air sucked into the engine is a bit warm.
Doom and gloom over, I've always had induction kits on my cars (not subaru) and found them ok. A cold air feed works a treat though.
Enjoy