OBDII Diagnostic Codes P0410, P0506, P0121, and P0507 in 2002 Olds Aurora 4.0L Engine at 178,000 km

The vehicle runs smoothly under normal conditions but exhibits erratic idle behavior: it may idle too low, stall when starting and shifting into gear, or stall while driving at slow speeds. In some cases, the engine idles too high and fails to respond properly to throttle input—instead of 'kicking down,' RPMs simply increase. These symptoms worsen in damp or humid weather. Multiple OBDII diagnostic codes have been detected: P0410 (Secondary Air Emission System Malfunction), P0506 (Idle Control Valve Performance Issue), P0121 (Throttle Position Sensor Range/Performance Fault), and P0507 (Fuel Pump Control Circuit Problem). It is suspected that the secondary air emission pump may be malfunctioning, potentially contributing to all these symptoms. The issue appears to be weather-sensitive and could stem from sensor or system-level failures in the engine management system.