The Idle Air Control Motor (IAC), also referred to as the Throttle Air Bypass Valve (TABP), is a stepper motor controlled by the vehicle’s onboard computer. The computer moves the pintle in and out of a bypass passage around the throttle blade to precisely regulate airflow at idle. This allows the engine to maintain a stable idle speed when varying loads—such as A/C operation, power steering input, or electrical demand—are placed on the engine.
How It Works:
- The vehicle’s ECU or PCM commands the IAC stepper motor to adjust pintle position
- The pintle opens or restricts the air bypass passage around the throttle blade
- This controlled airflow maintains the target idle speed under changing load conditions
- The ECU constantly monitors engine parameters to adjust the IAC in real time
- Proper IAC function ensures smooth idling and prevents stalling
Symptoms of a Failing Idle Air Control Motor:
- Engine surging or stalling
- Poor or unstable idle quality
- Idle speed too high or too low
- Hard starting or stalling immediately after start
- Check Engine Light on
Product Features & Benefits from Walker Products:
- Exact OE Fit – Direct-fit design ensures simple installation and correct alignment
- OE Replacement Quality – Manufactured to meet or exceed original performance
- Precision-Engineered Pintle Movement – Provides consistent, accurate idle control
- Durable Construction – Resists contamination, sticking, and long-term wear
- Restores Idle Stability – Improves drivability and proper air regulation
- Long Service Life – Designed to perform under varying load and temperature conditions
Common Check Engine Light (CEL) / OBD-II Codes
In accordance with the EPA’s OBD-II standards (adopted in 1996 and later expanded to heavy-duty applications), the following Diagnostic Trouble Codes (DTCs) are commonly associated with Idle Air Control Motor faults.
Use this list as a general reference only. Always consult a qualified technician and follow vehicle manufacturer and EPA guidelines for diagnostics, sensor replacement, and ECU/PCM relearn procedures.
- P0505 – Idle Air Control System
- P0506 – Idle Air Control System RPM Lower Than Expected
- P0507 – Idle Air Control System RPM Higher Than Expected
- P0508 – Idle Air Control System Circuit Low
- P0509 – Idle Air Control System Circuit High
- P050A – Cold Start Idle Air Control System Performance
- P050D – Cold Start Rough Idle
- P0511 – Idle Air Control Circuit
- P0518 – Idle Air Control Circuit Intermittent
- P0519 – Idle Air Control System Performance
- P2104 – Throttle Actuator Control System – Forced Idle
- P2176 – Throttle Actuator Control System – Idle Position Not Learned
- P2177 – System Too Lean Off Idle
- P2178 – System Too Rich Off Idle
- P2179 – System Too Lean Off Idle
- P2180 – System Too Rich Off Idle
- P2187 – System Too Lean at Idle
- P2188 – System Too Rich at Idle
- P2189 – System Too Lean at Idle
- P2190 – System Too Rich at Idle
- P256A – Engine Idle Speed Selector Sensor/Switch Circuit/Open
- P256B – Engine Idle Speed Selector Sensor/Switch Range/Performance
- P256C – Engine Idle Speed Selector Sensor/Switch Circuit Low
- P256D – Engine Idle Speed Selector Sensor/Switch Circuit High
- P256E – Engine Idle Speed Selector Sensor/Switch Circuit