P0506: The engine is idling too low
Idle Air Control System RPM Lower Than Expected
The idle speed is lower than it should be, so the car may stall at stops. Get it checked within a few days. If it stalls in traffic, have it towed.
Stop driving and get help if
- The check engine light is flashing
- The temperature gauge runs high, or you see steam (overheating)
- The car loses power, hesitates badly or stalls
- You smell burning or see smoke
- A brake warning light comes on, or the brakes feel different
Pull over as soon as you can, turn the engine off, and call a tow or roadside help.
What it means
P0506 means the engine's actual idle speed is consistently lower than what the computer is commanding. The computer is asking for a target idle RPM, but the engine cannot reach it. The most common reason is a restriction in airflow: carbon on the throttle body or IAC valve, or a vacuum leak that is confusing the system into overcorrecting. It can also happen when the idle load suddenly increases, such as when the AC compressor kicks in, and the engine cannot compensate quickly enough.
Common causes
- Carbon buildup on throttle bodyThe most common cause. Deposits restrict airflow at idle. Often fixes with a simple cleaning.
- Faulty or carbon-clogged IAC valveRestricts the bypass air that maintains idle speed under load.
- Vacuum leakCauses the idle to hunt and the PCM may overcorrect, resulting in a code.
- Clogged fuel injectors or low fuel pressureNot enough fuel at idle can pull the RPM down below target.
What the fix could involve
From the cheaper fix to the bigger one. Prices depend on your car, your area and the shop, so ask for a written quote that names the part and the labor before you approve it.
- Throttle body cleaning
- IAC valve cleaning or replacement
- Vacuum leak repair
Symptoms
- Low idle, engine may run at 400 to 500 RPM when it should be near 700 to 800
- Stalls at stops, especially when AC is on
- Rough idle
- Check engine light on
What to do next
Start with throttle body cleaning. It is cheap, takes less than an hour, and fixes P0506 more often than any other single repair. After cleaning, do the idle relearn procedure for your specific vehicle; many require it before the PCM will hold idle correctly again. Look up your vehicle's relearn steps before you start.
Lewis shows live idle RPM so you can see how far below normal the engine is idling and whether cleaning fixed the gap. Get Lewis on the App Store or Google Play.
Related codes
FAQ
- Is the idle relearn procedure really necessary?
- On many vehicles, yes. After cleaning the throttle body, some PCMs need to relearn the idle parameters. Skipping it can cause the idle to stay low even after a clean throttle body.
- Can P0506 cause the car to stall in drive?
- Yes. At low idle, adding load from the transmission in drive can pull RPM below the stall threshold. This is especially common when the AC is running.
- Is this different from P0505?
- P0505 is a general idle control system fault. P0506 specifically means idle is too low. Both often share the same causes and fixes.
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