P0506: Idle Air Control System RPM Lower Than Expected
The engine is idling slower than the computer is targeting, even after it tries to raise the idle.
What P0506 means
P0506 means the engine computer wanted a certain idle RPM, opened the idle air control or throttle further to get it, and the engine still idled too low. The most common reason is carbon. Over time, deposits build up around the throttle plate and in idle air passages, shrinking the opening the computer relies on for idle air. The computer adapts for a while, but eventually it runs out of range and sets the code. A failing idle valve, a sticking electronic throttle body, a clogged air filter or extra load from a bad accessory can also pull the idle down. After a battery disconnect, some cars lose their learned idle settings until a relearn is done. You may notice rough idle, vibration or stalling at stops, especially with the A/C on. Shops clean the throttle body, check for intake restrictions and vacuum leaks, watch the commanded idle position on a scan tool and run the relearn procedure.
Common symptoms
- Check engine light on
- Low or rough idle
- Stalling at stops or when A/C turns on
- Vibration at idle
- Hard starting in some cases
Most common causes
- Carbon buildup in the throttle body or idle valve
- Failing idle air control valve or electronic throttle body
- Restricted air intake or clogged air filter
- Heavy engine load from a failing accessory
- Idle relearn needed after battery disconnect
What to check yourself first
Check the engine air filter. Clean carbon from the throttle plate and bore with throttle body cleaner, following your owner manual. If the battery was disconnected recently, do the idle relearn procedure for your car.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Diagnosis, throttle body cleaning and idle relearn | $125-$183 | Throttle body cleaning and an idle relearn often fix low idle codes. |
| Replace throttle body | $623-$766 | If the electronic throttle body cannot open far enough. |
| Smoke test for vacuum leaks | $61-$90 | Rules out vacuum leaks that upset idle control. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
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Related codes
- P0505 Idle Air Control System
- P0507 Idle Air Control System RPM Higher Than Expected
- P0171 System Too Lean (Bank 1)
- P2135 Throttle/Pedal Position Sensor/Switch "A"/"B" Voltage Correlation
- P0300 Random/Multiple Cylinder Misfire Detected