I have an '02 WRX. My friend put a rather large K&N air filter on it. Now the 'Check Engine' light is on, and it will stall if I give it a lot of gas and then take it out of gear. Subaru Service told me it's code PO171 (system too lean). I'm assuming that if I can up the fuel, everything will be OK. Right? If so, what's the easiest way to do that?