96 Mazda 626 (check engine light) - Code: P0171?

Check air filter change if needed, check vacuum lines for leaks especially to pcv valve. fix any that may be leaking, if none found buy some foam type intake cleaner and clean MAF sensor and intake plenum, also check rubber intake hose for any splits. Usually one of these are the problem. O2 sensor just saying too lean because getting to much air not because it's bad.