What does it mean?
SPECIAL NOTE: While the definition “Cold Start Idle Air Control System Performance” seems to suggest that this code only applies to idle air control problems after start-up when the engine is cold, the fact is that many, if not most manufacturers have come to apply code PO50A to idle air control issues throughout the engine’s temperature range. END OF SPECIAL NOTE.
OBD II fault code P050A is a generic code that is almost universally defined as “Cold Start Idle Air Control System Performance”, or some variation of this definition, and is set when the PCM (Power Control Module) detects a signal from the Idle Air Control valve or its control system that falls outside of the accepted range in which the valve is expected to perform under any given set of circumstances.
The function of the Idle Air Control valve is to allow sufficient air into the engine to sustain a constant idling speed, and it does this by allowing atmospheric air to bypass the throttle plate (which is kept closed by the PCM), until the throttle is opened via the mechanism(s) that control it.
While Idle Air Control Valves take many forms and shapes, the principle of allowing air to bypass the throttle plate by means of an adjustable orifice is common to all, except in the case of “drive-by-wire” systems, where the PCM controls the throttle plate directly to allow sufficient air to enter engine past the throttle plate to sustain a steady idle.
Regardless of the design differences between Idle Air Control Valves (refer to the Troubleshooting section of this guide for more details), all are responsible for maintaining the quality of the engine idle. In practice, the PCM determines what can be termed the “desired idle speed”, which is a value that is programmed into the PCM as a PID (Performance Information Data), and which is accessible to most code readers.
Thus, when the engine starts, the PCM begins a process of comparing the desired idle speed with the actual idle speed, and when two values do not agree, the PCM activates a stepper motor in the idle air control valve to either enlarge, or reduce the effective size of the orifice through which air is bypassing the throttle plate, until the actual idle speed matches the desired idle speed.
However, any loads placed on the engine such as activation of the A/C system, power steering, or electrical consumers such as the wipers, headlights, and others, have the effect of lowering the idle speed. To counteract the effects of such loads, the PCM will command the idle air control valves’ stepper motor to adjust the effective bypass orifice to allow more air to enter the engine to increase the idle speed, and conversely, to reduce the orifice diameter when the loads are removed.
The Nett result of this is that the idle speed remains constant from start-up in subzero temperatures, all the way through to when the engine reaches operating temperature, regardless of the loads placed on the engine during idling. Note however, that changes to the Idle Air Control Valve’s settings are accompanied by adjustments to the fuel trim to compensate for the changing amounts of air that bypasses the throttle plate.
From the above, it should be obvious that the stepper motor, and its correct operation, is crucially important to maintaining the desired idle speed. When the PCM cannot control the idle speed effectively due to the poor performance of the idle air control valve or its control system, it will set code P050A, and illuminate a warning light. The image below shows the construction of a typical Idle Air Control Valve that uses a pintle to control the effective diameter of the bypass orifice.
Note however that not all Idle Air Control Valves use a pintle; in some cases, use is made of a rotary valve, or vacuum-operated diaphragm, that achieves the same thing, which is to control the amount of air that bypasses the throttle plate. Note the threaded pintle that passes through the armature- in designs of this type, the pintle is exten