1996 Honda Civic LX Idle Failure and P0171 Lean Code Solution

My 1996 Honda Civic LX with 155,000 miles has recently started experiencing intermittent slow idle or engine stalling when warm, while idling is normal during startup. Within a few weeks, the Check Engine Light illuminated and displayed code P0171 (System Too Lean). The vehicle was previously tuned up at around 100,000 miles under Honda's EPA settlement program, with a new catalytic converter installed. Spark plugs have been replaced since then, and the entire fuel system—including the fuel filter—is original. I understand that the idle bypass valve on 1996 Civics is a common repair (and often expensive), but I'm wondering if the P0171 lean code points more toward a fuel delivery issue rather than just the idle bypass valve. I'd appreciate hearing from others who have encountered this problem—especially with similar mileage and engine configurations. The Civic's fuel efficiency remains excellent today, which makes it a reliable daily driver despite these issues.