I've been working at Subaru for a while now and this stuff is boss!!
To get the best out of a can you spray 1/2 the can into plenum through the throttle body then let it sit in there for approx 5 min to let it take all the crap off then start the engine up (may take a few start ups to make it run, don't be worried if it coughs and splutters lol) give it a few revs, then once it's idling normally spray the other half of the can through the throttle body then hook all your piping etc back up and hold the revs at approx 3k until it stops blowing white smoke your car should run like a dream