# P0506: Idle Air Control System RPM Lower Than Expected **Verdict:** Safe to drive Speed and idle control - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $80-$900 - **Urgency:** Keep driving - **Most likely:** Carbon-clogged throttle body - **DIY?:** Yes, cleaning is easy ## Quick answer P0506 means the engine is idling slower than the computer is trying to make it idle, even after it has opened the idle air control as far as it can. The engine is not getting enough air at idle, usually because carbon has built up in the throttle body or idle air passage. You may notice a low, rough idle or stalling. ## What does P0506 mean? With your foot off the pedal, the engine computer holds the engine at a target idle speed by metering air past the closed throttle. Older engines do this through a separate idle air control (IAC) valve, and newer ones by opening an electronic throttle plate a tiny amount. The target changes with engine temperature and load, rising for a cold start or when the AC compressor switches on. P0506 sets when the engine idles below that target by more than an allowed amount for a set time, even though the computer is already asking for more air. That combination tells the computer something is choking off idle air or loading the engine down. The test runs with the engine warm and the car stopped. The thresholds vary by maker, and most cars need two failed drive cycles before the check engine light comes on. ## What are the symptoms of P0506? - Idle feels low, rough, or shaky - Engine stalls when stopping or when the AC turns on - Tachometer dips below normal idle - Check engine light on ## What causes P0506? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Carbon-clogged throttle body or idle air passage** (most common). Oil vapor from the PCV system and a little exhaust soot bake onto the throttle plate and bore, forming a black ring that narrows the gap air passes through at idle. Carbon builds slowly with mileage, and faster with short trips. The computer compensates until it runs out of range, then idle sags and P0506 sets. 2. **Sticking or failed idle air control valve** (common). On older engines with a separate IAC valve, carbon on the valve's plunger or a weak stepper motor can stop it from opening far enough when the computer asks for more air. Idle drops most noticeably when loads come on, such as the AC or the radiator fan. Cleaning sometimes frees it, but a worn motor needs replacement. 3. **Restricted air intake** (less common). A badly clogged air filter, a collapsed intake hose, or a duct blocked by leaves or a rodent nest reduces the air reaching the throttle. Idle needs only a little air, so it takes a severe restriction to cause P0506, but it is quick and cheap to rule out. Vehicles parked outdoors for long periods are most at risk. 4. **Extra engine load at idle** (less common). A seizing AC compressor, a failing alternator bearing, a tight power steering pump, or a dragging belt tensioner makes the engine work harder at idle. If that load is more than the idle control can overcome, RPM falls below target. Noise from the belt area, or idle that drops only with the AC on, points here. 5. **Failing electronic throttle body** (rare). On drive-by-wire engines, the throttle body's small motor and gears set the throttle opening at idle. Worn gears or a weak motor may not open the plate far enough, sometimes only once the engine is hot. This is rare and usually comes with throttle actuator or position codes, so shops test it only after cleaning fails. ## How do you diagnose P0506? 1. Inspect the throttle body and idle air passage for carbon. 2. Check the air filter and intake duct for blockages. 3. Watch idle speed and idle air control commands with a scan tool, including with the AC on and off. 4. Check for heavy loads from belt-driven accessories. ## How do you fix P0506, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Clean throttle body and idle passage | $80-$180 | Often fixes P0506. A scan tool idle relearn may be needed afterward. | | Replace idle air control valve | $150-$400 | For older cars with a separate valve that has failed. | | Replace electronic throttle body | $350-$900 | Only if cleaning does not help and the throttle body tests faulty. | ## Is it safe to drive with P0506? > **Safe to drive.** It is generally safe to drive. Fix it sooner if the engine stalls at stops, since stalling makes steering and braking harder. ## Will P0506 fail an emissions test? A lit check engine light with P0506 stored fails an OBD-II emissions test in most states. Low idle by itself does not usually change tailpipe readings, but clearing the code also resets the readiness monitors, so the car may be rejected as not ready. Clean or repair first, then allow several days of normal driving before the test. ## After the repair: clearing P0506 After cleaning the throttle body, clear the code and perform the idle relearn your car calls for. Without it, some engines idle too high, too low, or stall for a while, because the computer still expects the old, restricted airflow. A successful fix shows a steady warm idle at the normal speed, including with the AC running. ## How to prevent P0506 - Clean the throttle body when idle begins to sag, before carbon builds up enough to stall the engine. - Replace the engine air filter on schedule and check the intake duct for leaves or debris. - Keep the PCV system working, since oily crankcase vapor is a main source of throttle carbon. - Fix squealing belts or noisy accessories early, because a dragging accessory pulls idle speed down. - Check your manual before cleaning, since some makers warn against solvents on coated throttle bores. ## Codes often seen with P0506 - [P0505](/codes/p0505): Idle Air Control System - [P0507](/codes/p0507): Idle Air Control System RPM Higher Than Expected - [P0121](/codes/p0121): Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance ## Frequently asked questions ### Can I drive with a P0506 code? Yes, P0506 is usually not urgent, and many cars drive normally apart from a low or rough idle. If the engine stalls when you stop or turn, get it repaired sooner, because a stalled engine loses power steering assist, and brake assist fades after a few presses of the pedal. ### How do I clean a throttle body? With the engine off, remove the intake duct, spray throttle body cleaner on a rag, and wipe the carbon from the bore and the edges of the throttle plate. Do not force open an electronic throttle by hand or soak its electronics. Check whether your car needs an idle relearn afterward. ### Can a dirty air filter cause P0506? It can contribute if the filter is badly clogged, but it is not the usual cause, and a dirty throttle body is far more common. Since an air filter costs little and takes minutes to check, it is still a sensible first look before cleaning the throttle body or testing the idle air control. ### How much does it cost to fix P0506? Most P0506 repairs cost $80 to $180, the price of a throttle body cleaning and idle relearn at a shop. Replacing a failed IAC valve on an older car costs about $150 to $400. A new electronic throttle body runs about $350 to $900, but it is needed only if cleaning fails. ### What is the difference between P0506 and P0507? P0506 means idle is lower than the computer wants, and P0507 means it is higher. Low idle usually points to a restriction, such as carbon in the throttle body, or to extra engine load. High idle usually points to extra air getting in, most often a vacuum leak, so the fixes differ. ### Why does my car stall when I come to a stop? When you stop, the throttle closes and the computer must catch the falling RPM with idle air. If carbon has narrowed the idle air path, there is not enough air to catch it, especially with the AC or power steering adding load, and the engine stalls. That is classic P0506 behavior. ### Can I fix P0506 myself? Usually yes, because the most common fix is cleaning the throttle body, which many owners do with a can of throttle body cleaner, a rag, and basic tools in under an hour. If your car needs a scan tool idle relearn afterward, a shop can do it quickly. Throttle body replacement is harder. ### Will P0506 fail an emissions test? Yes, in most OBD-II testing states any stored code with the check engine light on is a fail, and P0506 is no exception. Clearing the code before the test also resets the readiness monitors. Fix the idle, clear the code, and drive normally for several days so the monitors finish. ### Can disconnecting the battery cause P0506? It can on some cars. Disconnecting or replacing the battery erases the learned idle settings, and an engine with a slightly dirty throttle body may idle low until it relearns. An idle relearn, or several minutes of idling with accessories off, often fixes it. If the code returns, clean the throttle body. ### Is it safe to clean an electronic throttle body? Usually yes, with care. Turn the ignition off, never push the plate open with your fingers while the key is on, and keep cleaner away from the motor and sensor. A few makers warn against solvents on specially coated throttle bores, so check your service manual before cleaning. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) ## Other speed and idle control codes - [P0500 Vehicle Speed Sensor "A"](https://diagxcar.com/codes/p0500) - [P0505 Idle Air Control System](https://diagxcar.com/codes/p0505) - [P0507 Idle Air Control System RPM Higher Than Expected](https://diagxcar.com/codes/p0507) - [P0520 Engine Oil Pressure Sensor/Switch "A" Circuit](https://diagxcar.com/codes/p0520) - [P0521 Engine Oil Pressure Sensor/Switch "A" Circuit Range/Performance](https://diagxcar.com/codes/p0521) - [P0522 Engine Oil Pressure Sensor/Switch "A" Circuit Low](https://diagxcar.com/codes/p0522) - [P0523 Engine Oil Pressure Sensor/Switch "A" Circuit High](https://diagxcar.com/codes/p0523) - [P0524 Engine Oil Pressure Too Low](https://diagxcar.com/codes/p0524) - [P0562 System Voltage Low](https://diagxcar.com/codes/p0562) - [P0571 Brake Switch "A" Circuit](https://diagxcar.com/codes/p0571) - [P0402 Exhaust Gas Recirculation "A" Flow Excessive Detected](https://diagxcar.com/codes/p0402) ## Symptoms - [Why is my car idling rough?](https://diagxcar.com/symptoms/rough-idle) - [Why does my car stall while driving?](https://diagxcar.com/symptoms/car-stalls-while-driving) - [Why does my car shake at idle?](https://diagxcar.com/symptoms/car-shakes-at-idle) --- Source page: https://diagxcar.com/codes/p0506 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.