Crucial to the function of your vehicle, the idle air control system manages engine idle speed. Along with maintaining a steady engine speed at idle, this system also warms your vehicle up in the mornings. When a component of the idle air control system goes awry, your onboard computer will trigger your MIL, turning your check engine light on with the P0508 code.
Should you find your check engine light on, the use of an OBDII scan tool can retrieve your error. If you have a P0508 trouble code, you will need to track down the root cause of this error. Before you begin, you’ll need to understand what P0508 means.
What Does P0508 Code Mean?
The proper definition of the OBDII code P0508 is Idle Air Control System Circuit Low. This means that the signal of the circuit to your idle air control system is too low, affecting your Powertrain Control Module’s ability to regulate idle engine speed.
When your vehicle is started, your PCM / ECU helps maintain the proper idle by allowing more or less air into your engine. In older vehicles, this is accomplished by way of machined passages in your intake manifold. For newer models, this idle air control system is part of your electronic throttle body.
In both cases, however, the P0508 error code means that there’s a fundamental issue with a component of your idle speed controller. The P0508 problem can range from an internal valve, or blocked passages in your intake system.
Symptoms of the P0508 code
- Engine idle is too low or erratic – This is one of more common symptoms of this error. Should your vehicle idle become erratic, you could also encounter another OBDII trouble code P0506 – Idle Air Control System RPM Lower Than Expected
- Engine idle is too high – Similar to the P0506 OBDII trouble code, too high of an idle or an uncontrollable one is a huge problem as well. There could also be another check engine light stored in your system, like the P0505 – Idle Air Control System trouble code.
- Engine stalls when coming to a stop
How to troubleshoot idle problems
Determine what kind of idle control system your vehicle has – Owning a vehicle with an electronic throttle, versus an older traditional one will change the way you troubleshoot this issue.
Traditional throttle bodies – You will need to check and set the idle speed of your vehicle before you begin. If there is a problem with idle surge, you can begin by checking your air idle control valve first.
Electronic throttle bodies – These are a bit trickier to troubleshoot, as most of the components are housed as one. You can still do things like testing your idle air control externally to your throttle body however. If need be, you can also replace the idle air controller, or reprogram your throttle body at the dealership.
Common causes of P0508 Code
As previously stated, there can be many issues that lead to the dreaded P0508 check engine light. Some of these causes are listed below.
- Idle Air Control (IAC) valve failure – When this valve fails, you’ve developed a leak or a clog that prevents your PCM / ECU from doing its job properly
- Vacuum leak – These are the easiest to track down, with the proper use of a spray bottle filled with soapy water. Carefully spray around your hoses to determine the nature of your leak. Replace the air hoses and retest using an OBDII scan tool to erase the MIL status of your ECU.
- Air Filter Clogged – In some extreme cases, idle issues can arise from a completely clogged up air filter.
