P0511 – Idle air control (IAC) -circuit malfunction

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By Tapley Mitchell (Contact Me)
Last Updated 2019-09-25
ASE Mechanic
CodeFault LocationProbable Cause
P0511 Idle air control (IAC) -circuit malfunction
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Wiring, poor connection, lac valve, ECM

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Table of Contents

  1. What Does Code P0511 Mean?
  2. What are the common causes of code P0511 ?
  3. What are the symptoms of code P0511 ?
  4. How do you troubleshoot code P0511 ?
  5. Codes Related to P0511
  6. Get Help with P0511

What Does Code P0511 Mean?

Idle air control does just as its name suggests and controls the idle by allowing a certain amount of air to enter the engine. This keeps the idle at a specific RPM, and helps the engine to run better, and last longer. When the throttle body is closed, a very small amount of ambient air can get by the throttle plate. This gives the idle control to the IAC, which is a device that uses a plunger to monitor the amount of air that goes into the engine. Air is controlled by feedback circuits that control the IAC and only allow the amount of air that is necessary. As the plunger moves it allows for either more air or less air as per the needs of the engine determined by the ECU.

What are the common causes of code P0511 ?

While it is likely that your intake idle control has failed, don’t be too hasty to replace it until you have checked all of the following.

  • Wiring and connectors for the IAC circuits.
  • Vacuum leaks in the intake system
  • Excessive EGR buildup
  • Restricted throttle body
  • Dirty or restricted MAF sensor
  • Faulty ECU

What are the symptoms of code P0511 ?

  • Check engine light – on
  • Noise coming from the intake, and throttle body area
  • Engine idle too high or too low
  • Hissing noise in engine bay
  • Rough idle, possibly stalling (especially in gear or when A/C is on)

How do you troubleshoot code P0511 ?

Using a scan tool check the freeze frames, and any other codes that may be present. Write down some of the critical values shown in the freeze frame (IAT, ECT, RPM, Run Time, TP, etc) this can aid in repeating the situation where the IAC failed. Next clear the codes and attempt to get them again by recreating the same values you found on the freeze frames. If you do not get any additional codes, you could have an intermittent issue. These are particularly difficult to pinpoint, but should become more aggressive as the vehicle is used. Once you have verified the problem, continue onto diagnosis.

Before beginning diagnosis on your vehicle start by looking up you specific vehicle’s info on a reliable database (All Data, Prodemand) and check for TSB or Technical Service bulletin, or recalls that may be related to your issue. If you find a TSB related to your IAC issue, the manufacturer will have a verified fix that may solve your problem easily and quickly. If there is not a TSB or it did not fix the problem, let’s start with the wiring.

Check the wiring for any corrosion, especially around connectors, and anywhere the wires may be exposed (grounds, splices) also look for melted, cut or worn insulation, which could cause a short to ground. Next using a DMM (Digital MultiMeter) check for the proper amount of voltage at the IAC connector. If you have the right voltage, your wiring may be ok. Also check the resistance values of you IAC this could indicate if the stepper motor is failing by having too high or too low of resistance.

One of the best ways to verify the problem is directly related to the IAC is to carefully remove the IAC (to not damage the gasket) and use something to cover the opening, such as a piece of cardboard, rubber, wood, or even your fingers. With the engine running move the covering to allow more or less air into the engine. If you can successfully control the engine idle by doing this, the problem is most likely directly related to the IAC. While you are performing this test, check to see if the plunger is moving inside the IAC as you control the airflow.

Next look for vacuum leaks this can be caused by any amount of air being introduced to the engine AFTER the MAF (Manifold Air Flow) sensor, which is found next to the air filter in most cases. Check all vacuum hoses and lines, especially the larger ones such as: brake booster, PCV, vacuum canister, and evap control lines. Also check the intake manifold, egr, throttle body, and IAC gaskets for leaks.

The final cause (which is also very rare) is the most expensive in most cases, and the most difficult to diagnose, this is an internal failure of the ECU. Using an ECU from another identical vehicle, may not even be possible due to VIN programming and other manufacturer security measures. If you have thoroughly checked all other possible causes, and still have an issue, I would recommend taking your vehicle to the dealer before replacing the ECU (especially if you do need a new ECU since they will be the best option to reprogram your ECU).

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