P050A – Cold Start Idle Air Control System Performance

By Reinier (Contact Me)
Last Updated 2016-11-03
Automobile Repair Shop Owner

Table of Contents

1. What Does Code P050A Mean?
2. What are the common causes of code P050A?
3. What are the symptoms of code P050A?
4. How do you troubleshoot code P050A?
5. Codes Related to P050A
6. Get Help with P050A

What Does Code P050A 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 extended or retracted when the armature rotates. Also, note that regardless of their design, Idle Air Control Valves are always located on, or near the throttle body.

What are the common causes of code P050A?

NOTE: The causes of a poor idle are many and varied, and for the most part make and model specific. However, while some possible causes of this code are common to all applications, the list of possible causes presented here may not be complete. Also, note that not all causes listed here will have the same effect on all applications.

• Carbon build-up on the valve pintle, and/or throttle body
• Defective idle air control valve/stepper motor
• Broken, cracked, split, or mis-installed inlet air ducting
• Clogged or dirty air filter element
• Unmetered air entering the engine through leaks or other defects in the vacuum system
• MAF sensor failure
• Intake air temperature sensor failure
• Engine coolant sensor failure
• Malfunctions in, or poor performance of ignition system components/systems

What are the symptoms of code P050A?

Possible symptoms of code P050A vary between slight and barely detectable, to severe driveability issues that can effectively render a vehicle un-driveable. Other possible symptoms may include the following-

• Stored trouble code and an illuminated warning light
• Rough idle that may vary in severity between applications, depending on the exact nature of the cause
• High idle that exceeds the “desired” idle speed
• Low idle that falls below the “desired” idle speed
• Erratic or fluctuating idle speed, especially when additional loads are placed on the engine during idling
• Frequent or unpredictable stalling when the vehicle is stopped
• Complete failure to idle at all

How do you troubleshoot code P050A?

SPECIAL NOTES: Due to the large number of Idle Air Control Valve designs (and a correspondingly large number of different control systems) in use today, it is not possible to provide detailed diagnostic and repair information for each type of Idle Air Control Valve here. Performance information data (PID’s), as well as diagnostic and repair procedures for each type of valve are mostly make and model specific, which means that attempts to diagnose and/or repair code P050A should NOT be made without a repair manual for that application being close at hand.

In terms of specific differences between Idle Air Control Valves, it should be noted that apart from outward appearances, there are fundamental differences between the windings of stepper motors used in these devices. The two main types of windings in use today are; “permanent magnet motors”, and “variable reluctance motors”, both of which are briefly described below-

• Permanent magnet stepper motors- Stepper motors of this type usually have two independent windings that may or may not have center taps. Windings with center taps are used in uni-polar permanent magnet motors as used in many Chrysler applications

.

• Variable reluctance stepper motors- Depending on the application, variable reluctance motors usually have three windings (but can sometimes have four), with a common return.

These internal differences are not apparent by merely looking at the stepper motor, but more importantly, the testing procedure(s) that apply to each type are different, which can make it difficult to determine whether a particular motor is defective or not if specific, relevant, and accurate reference data for the application is not available. END OF SPECIAL NOTES.

NOTE #1: Non-professional mechanics should be aware that for the most part, there are three distinct types of Idle Air Control valves in use today, each of which is briefly described below-

• Stepper motor type- Unlike electric motors that rotate continuously when they are energized, stepper motors only rotate a few degrees each time it receives an electrical pulse. Depending on the design, one stepper motor may rotate say, 5 degrees for each signal receives, while another may rotate 10 degrees for each signal, or pulse. By rotating only a few degrees for each pulse received, the pintle that controls the airflow through the valve can be controlled very precisely, with the pitch of the screw thread on the pintle determining the actual amount by which the pintle is extended or retracted for each degree of rotation of the motor. In valves that use rotary spindles, the degree of rotation is determined by the gearing of the spindle.

However, to make large adjustments to the engine idling speed, the PCM delivers a series of pulses to produce large degrees of rotation; the more the motor rotates the further the pintle extends or retracts, which produces the desired changes in the idling speed by increasing, or reducing the airflow through the valve. In diagnostics parlance, the number of pulses received translates into a value that is displayed by a scanner as the “IAC COUNT”. The higher or lower the displayed IAC count, the more (or less) air is being passed through the valve and therefore, the higher or lower the idling speed.

• Duty cycle controlled valve- Valves of this type work on the principle of a “duty cycle”, which is best described as the percentage of time it is receiving a series of rapid pulses, as opposed to the time during which it not receiving pulses. For instance, if the motor winding receives a series of pulses for 1 second out of every 10 seconds, the duty cycle is 10%, which 10% represents the valves’ “working”, or “ON” time. Code readers display the duty cycles of such a valves as “IAC percentages”, and the higher the displayed percentage, the longer the valve’s duty cycle.

• DC motor-controlled valve- As the name suggests, this type of valve is controlled by a DC motor that opens and closes the actual throttle plates via a connecting rod that is attached to both the motor and the throttle plate(s). These valves are controlled by a switch that is incorporated into the motor; every time the switch comes into contact with the throttle plate lever, the switch either opens or closes, which state is displayed by code readers as an “ON/OFF” This type of valve is commonly found on Cadillac models, as well as on some Korean imports.

• Mechanical coolant temperature activated valve- Valves of this type are controlled by the engine coolant temperature, and they are generally only active while the engine is warming up. However, as with other types of Idle Air Control Valves, the engine idle will suffer if the valve is not working properly.

NOTE #2: Engine idling problems on many Ford applications are often caused by the EGPD (Exhaust Gas Pressure Differential Valve), also sometimes known as the DPFE (Delta Pressure Feedback of EGR Sensor on some Ford applications). This device is not directly related to the idle sped control system, but when it malfunctions (which happens often), it activates the EGR (Exhaust Gas Recirculation) system. When this happens at the wrong time, such as when the engine is idling, the idle quality is seriously affected by the introduction of exhaust gas into the inlet tract. It is therefore always a good idea to start with checking, or replacing the EGPD valve whenever idling issues are encountered on Ford products. The image below shows a typical EGPD valve on a Ford application- note the two rubber tubes leading into the valve.

NOTE #3: It is fair to say that carbon build-up on valve pintles, as well as inside the air bypass passages is the leading cause of idling problems on most applications. Therefore, it is always a good idea to start a diagnostic/repair procedure for code P050A (or any other idling related code) with an inspection of the valve for the presence of carbon deposits. In most cases, the carbon can be removed from the pintle and passages relatively easily with an approved solvent, which will resolve this code nine times out of every ten.

Note #4: As stated previously, this guide cannot provide detailed diagnostic/repair procedures for all applications. However, the few “generic” steps outlined below should enable the average DIY mechanic to successfully diagnose and repair code P050A.

Step 1

Record all fault codes present, as well as all available freeze frame data. This information can be of use should an intermittent fault be diagnosed later on.

NOTE: If other codes are present along with P050A, and especially code P050B, -“Cold Start Ignition Timing Performance”- it is important to resolve these codes in the order in which they were stored before attempting to diagnose P050A. In some cases, it is possible to resolve P050A by resolving one or more other codes, but bear in mind that on some applications, there are up to 30 or more codes that could trigger, or contribute to setting P050A. Consult the manual for detailed information on which other codes are likely to contribute to P050A being set, but it is highly unlikely that all, or even most of them would be present at any one time.

Step 2

If resolving all other codes did not resolve P050A, consult the manual to locate the Idle Air Control Valve, and follow the instructions provided to remove the valve from the engine, and inspect the valve for the presence of carbon deposits.

Use an approved solvent to clean all carbon deposits off all visible surfaces, and don’t forget to clean the area around the pintle seat as well. If required, remove the throttle body from the inlet tract to be able to clean out all carbon deposits from all internal surfaces, paying particular attention to the air passages running through the throttle body. Use compressed air to blow-dry all surfaces, and to make sure all carbon residues are removed. A household vacuum cleaner set to “blow” works rather well for this.

Step 3

Once the valve and throttle body are clean, reattach the valve’s wiring, and make sure the unit is properly grounded for the next step to work.

Use the scanner to command the valve open and then closed, and note how the pintle or other regulating device reacts to control inputs, but do NOT turn the pintle by hand at this point, since doing so will upset the position the PCM has “learnt” the position the pintle is in when it is in the closed position.

NOTE #1: All stepper motors have a set number of “steps” that it can be at from fully retracted, to fully extended, but be aware that this number of steps varies between applications. Nonetheless, when the pintle is fully extended (closing the valve) the code reader should indicate this by displaying the minimum value (usually “0”, and the maximum number of steps (or very close to it), when the pintle is fully retracted, and the valve is fully open. Consult the manual to determine the number of steps for the application being worked on, and activate the stepper motor several times with the code reader to verify that the pintle does in fact reach both the fully retracted and extended positions.

Replace the stepper motor/valve combination if the scanner indicates different “step” values when the pintle should be fully retracted or extended. Bear in mind though that the PCM may have to “relearn” the replacement valves’ closed position before the code can be cleared. Consult the manual on the correct procedure to adapt the valve to the PCM if this is required.

NOTE #2: In some cases, it may be necessary to measure the distance between two points on the pintle/valve body to be sure the valve still conforms to the manufacturer’s specifications. If this is required, be sure to follow the directions in the manual EXACTLY, and replace the valve if the specified distance varies from the actual, measured distance. Refer to the note above with regard to adapting the replacement valve to the PCM.

Step 4

If the previous steps did not reveal any discrepancies, refit the valve/throttle body, clear all codes, and rescan the system to see if the code returns. Bear in mind that most applications have a set procedure that has to be followed before either the code can be cleared, or the system re-scanned to see if the code persists. Consult the manual on the correct procedure.

Step 5

If the code persists, consult the manual to determine the location, function, routing, and color-coding of all associated wiring, and perform a thorough visual inspection of said wiring. Look for damaged, burnt, shorted, corroded, or disconnected wiring and connectors. Make repairs as required, and retest the system to see if the code returns.

NOTE: Be aware that on some applications, it may be necessary to remove insulation from one or more harnesses to gain access to all associated wiring. Use extreme caution during this process to avoid causing damage where there was none before.

Step 6

If no visible damage is found, prepare to perform reference voltage, continuity, ground, and resistance checks (in strict accordance with the instructions in the manual) on all relevant wiring and connectors, and be sure to test the resistance of the stepper motor or other control device as well. Be sure however to disconnect the valve from the PCM and other controllers to avoid damage to the controller(s) during this step.

Compare all obtained readings with the values stated in the manual, and if discrepancies are found, make repairs as required to ensure that all values fall within specified ranges. Retest the system after repairs are complete. If the code persists at this point, suspect a faulty PCM, or a particularly stubborn intermittent fault.

NOTE: While PCM failure is not altogether impossible, it is far more likely that the problem is still being caused by an intermittent fault. Be aware though faults of this type can sometimes be extremely challenging to find and repair, and in some cases, the fault may have to be allowed to worsen before an accurate diagnosis and definitive repair can be made.

Step 7 (Some notes on hysteresis settings)

Idling problems are among the most vexing of all car troubles, which is aggravated by the fact the idling control system is one of the slowest systems to react to control inputs on any application. Therefore, if none of the steps outlined above resolve the problem, it might be worth the time and effort to look at the hysteresis settings of the control system in an effort to identify the root cause of the poor idle.

“Hysteresis” is a general term used in the control systems that refers to the amount by which something must change before something else will change, and as such, hysteresis can be seen as the “underpinnings” of the idle control system. For instance, since stepper motors only rotate by a fixed number of degrees per input signal, the input signal must be valid before the stepper motor will rotate by that amount, or rotate at all.

Put in another way, this means that if the stepper motor requires say, ten pulses for the pintle to be moved by “X” amount, either the number of pulses, or the quality of the pulses (or both), have a direct bearing on how much air the valve lets through in any given amount of time. Hysteresis settings are usually programmed into the PCM, but the problem with this is that not all code readers can access this part of the PCM, which means that a poor idle might not be the result of component failures, but rather as the result of corrupted control inputs, which are seldom detectable with conventional testing methods using only a multimeter.

In essence, this means that the idle air control system might be working perfectly, but in response to corrupted or invalid control inputs from the PCM. The only reliable way to determine if this is the case is to use a lab grade oscilloscope to obtain waveforms generated by the idle air control system that can be compared to the manufacturers’ reference data.

Non-professional mechanics seldom have access to either an oscilloscope or the manufacturers’ reference data, meaning that in cases where poor idling is persistent or particularly difficult to diagnose, referring the vehicle for professional diagnosis and repairs might be the only viable option available to non-professionals.

Codes Related to P050A

• P050B – Relates to “Cold Start Ignition Timing Performance”.

NOTE: Code P050B refers to the fact that the ignition timing is retarded during the initial warm-up period after starting a cold engine. In practice, the ignition timing is retarded for a set period in order to increase the temperature of the catalyst (in the catalytic converter) to reduce emissions, hence the close relationship between P050A and P050B.

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