P0506: Idle Control System RPM Lower Than Expected
P0506 means the engine's idle speed (the RPM at standstill with the engine warm) is staying below the target, even though the computer is doing all it can to raise it. It is usually not an emergency, but a low idle can lead to stalling, so get it checked soon.
You can drive, but get it checked soon
The car usually keeps running, and the data does not list limp mode for this code. A low idle can make the engine shake or stall when you stop or turn on the A/C, which is a risk in traffic, so avoid long drives and have it looked at soon.
What it means
The engine computer sets a target idle speed and adjusts air intake to hold it. Older engines use a separate idle air control valve that lets a small amount of air bypass the closed throttle. Engines with an electronic throttle control idle with the throttle itself and have no separate valve. P0506 is stored when the warm engine at standstill idles too low despite the control system using its full range of correction. The thresholds differ by manufacturer, for example GM and Ford each use their own rpm and timing limits. The check engine light comes on after the fault is detected, and on some vehicles it takes two trips. Common reasons are deposits in the air path, extra load on the engine, or a restricted intake or exhaust.
Likely causes
- Deposits at the throttle or bypass channel, or gummed idle valveVery likely
Buildup restricts the air the engine needs at idle, so the computer cannot raise the speed to the target.
- Extra load: stiff accessory drive, gearbox or converterPossible
Anything that makes the engine work harder at idle can pull the speed below target.
- Intake or exhaust restricted (air filter, catalyst)Possible
If air cannot flow in or exhaust cannot flow out freely, the engine cannot hold its idle speed.
- Idle valve or throttle actuator faulty, wrong learned valuePossible
A failing actuator or an incorrect learned idle value stops the computer from setting the right air amount.
- Mechanical engine damage (low compression)Less likely
An engine that has lost compression produces less power at idle and may not reach the target speed.
What you may notice
- Idle is too low and the engine shakes
- Engine stalls when you stop or when the A/C is on
- Check engine light comes on after two trips
What to check, cheapest first
- 1Read the stored codes and look at related ones such as P0505, P0507, P050A, P2111 and P0171, which can point to the same air-flow problem. · you can do it
- 2Inspect the air filter and replace it if it is dirty or clogged. · you can do it
- 3Check that the accessory drive belt and pulleys turn freely and that the belt is in good condition. · you can do it
- 4Clean the throttle body and the idle bypass channel or idle valve if your car has one, following the service instructions for your vehicle. · you can do it
- 5Check the idle valve or throttle actuator and perform an idle relearn with a scan tool if the value is wrong. · mechanic
- 6Test for a restricted exhaust or catalyst, for extra load from the gearbox or converter, and for low compression if nothing else explains it. · mechanic
Related codes
Frequently asked questions
Can I drive with a P0506 code?+
Usually yes for short trips, but the engine may stall when you stop or use the A/C. Have it checked soon.
Can a dirty throttle body cause P0506?+
Yes. Deposits at the throttle or bypass channel are the most likely cause, and cleaning is often the first repair.
Will P0506 fail an emissions test?+
It can. The code is emissions relevant and turns on the check engine light, which normally causes a failure until it is fixed and the car completes its drive cycle.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10