1999 Ford Explorer P0171 and P0174 Codes: MAF Cleaned, Vacuum Check Complete, EGR Solenoid Still Shows Pulsating Vacuum at Idle

I recently cleaned the Mass Air Flow (MAF) sensor and performed a thorough vacuum leak check on the intake system—both tests came back negative. However, the vehicle continues to display OBD2 diagnostic codes P0171 (Rich Mix Bank 1) and P0174 (Rich Mix Bank 2). During my inspection, I noticed that the EGR solenoid was supplying a small, pulsating vacuum signal to the EGR valve at idle. When I unplugged the EGR solenoid, the vacuum presence remained unchanged—indicating the system is still receiving vacuum. Given this observation, could the persistent P0171 and P0174 codes be directly related to the EGR system behavior? I'm seeking input on whether this symptom might trigger these specific fault codes in a 1999 Ford Explorer.