2001 Ford F-150 4.2L V6 - OBD2 P0171 & P0174 Codes: Lean Mixtures, Low Idle, Knocking After MAF Replacement

My 2001 Ford F-150 2WD with a 4.2L V6 engine and 5-speed manual transmission has developed check engine light issues. The OBD2 diagnostic tool returned both P0171 (System Too Lean Bank 1) and P0174 (System Too Lean Bank 2), indicating lean air-fuel mixtures on both engine banks. I initially tried cleaning the Mass Airflow (MAF) sensor, which improved idle stability slightly. However, I found no cracked or collapsed vacuum hoses—Ford's design hides these behind the firewall, between the cylinder block and intake manifold. After replacing the MAF sensor, some idle issues were resolved, but a persistent hard knocking sound remains, especially when accelerating. The engine also exhibits a noticeable rise in RPM when the clutch is depressed, suggesting an unbalanced load or lean condition. I noticed that the Positive Crankcase Ventilation (PCV) valve was partially dislodged from its housing and reseated it properly. Since then, the check engine light has not reappeared, but I now experience low idle problems—when the clutch is engaged, the RPM drops to 200–300 rpm and only returns to normal after about 10 seconds. Any insights or suggestions on how to address this lean condition and stabilize idle performance? Could it be related to fuel pressure, intake leaks, or a faulty oxygen sensor?