Cause
Binding throttle plate or linkage
A throttle plate or its linkage stiff in its bore, so the actuator cannot move it freely to the commanded position. The module detects it by comparing command against feedback and reports a throttle actuator or idle control fault, which reads as an electrical problem in a part that is mechanically stuck.
Carbon is the usual cause and it accumulates where it matters most. Deposits build around the plate's edge and on the bore at the closed position — precisely where idle is controlled — so the fault shows worst at idle and light throttle and may be unnoticeable at larger openings. An unstable idle with normal wide-open performance is this pattern.
Cleaning is the repair, with two cautions. Many electronic throttle bodies have a coating that solvent and abrasion will remove, making the surface rougher and the problem worse, so use what the manufacturer permits. And cleaning almost always requires a relearn afterwards — the module has adapted to the old closed position over years, and removing the carbon changes it. Skipping the relearn produces a fresh set of codes on a throttle body that has just been correctly cleaned.
Typically a moderate job.
Some of these codes mean you should stop driving
2 of the 6 codes this can cause indicate a fault where continuing to drive risks damage or is unsafe. Which one you have matters more than the cause does — read the code's own page before deciding.
Codes this can cause (6)
Codes where this is a likely explanation first, rather than merely a possible one.
- P0121 Throttle/Pedal Position Sensor/Switch A Circuit Range/Performance Stop driving High
- P0221 Throttle/Pedal Position Sensor/Switch B Circuit Range/Performance Stop driving High
- P0505 Idle Air Control System Moderate
- P0506 Idle Air Control System RPM Lower Than Expected Moderate
- P0507 Idle Air Control System RPM Higher Than Expected Moderate
- P0638 Throttle Actuator Control Range/Performance — Bank 1 High
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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