P0506: Idle Air Control System RPM Lower Than Expected
Updated November 13, 2026
The engine computer has a target idle speed and adjusts airflow to hold it. P0506 means the actual idle stays below the target even though the computer is trying to raise it, usually because not enough air is getting past the throttle at idle.
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🔧 Want to check this yourself? An OBD2 scanner reads the code; models with live data also show the sensor readings used in the checks below. See code readers and scanners from $24.99 ↓ · Which scanner do I need?
Common causes
- Carbon or varnish buildup in the throttle body or idle air passages
- A sticking or failed idle air control (IAC) valve on engines that have one
- A faulty electronic throttle body
- An idle relearn not done after cleaning the throttle body or disconnecting the battery
- Extra engine load at idle, such as a dragging accessory
Code meanings can vary slightly by manufacturer. Use these as a starting point and confirm with your vehicle's service information or a mechanic before replacing parts.
Symptoms
- Low or rough idle
- Engine feels like it wants to stall at stops
- Stalling, especially with the AC on or when coming to a stop
Is it safe to drive?
If the engine stalls, don't drive it until it's fixed; stalling in traffic is dangerous. If it only idles a little low and doesn't stall, it's usually OK to drive while you get it checked.
How to check it with a scanner
- Plug an OBD2 scanner into the port under the dashboard and read all stored codes and the freeze-frame data (the conditions when the code set).
- Scan for other codes, such as throttle, MAF or misfire codes, and fix those first.
- With the engine off and the key out, inspect the throttle body for carbon buildup. On electronic throttles, don't force the throttle plate open by hand; follow your vehicle's cleaning procedure, and don't turn the key on while your fingers are near the plate.
- After cleaning the throttle body or replacing parts, perform your vehicle's idle relearn procedure.
- Keep hands clear of the belts and fan when the engine is running.
- After a repair, clear the code and drive normally for a few days to confirm it doesn't come back.
A basic code reader shows the code; scanners with live data let you watch sensor readings, which is what you need for most of the checks above. See OBD2 scanners under $100.
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Questions
What does P0506 mean?
P0506 is the generic OBD2 code for "Idle Air Control System RPM Lower Than Expected." The engine computer has a target idle speed and adjusts airflow to hold it. P0506 means the actual idle stays below the target even though the computer is trying to raise it, usually because not enough air is getting past the throttle at idle.
Is it safe to drive with P0506?
If the engine stalls, don't drive it until it's fixed; stalling in traffic is dangerous. If it only idles a little low and doesn't stall, it's usually OK to drive while you get it checked.
How do I check P0506 myself?
Read the code and freeze-frame data with an OBD2 scanner, then: Scan for other codes, such as throttle, MAF or misfire codes, and fix those first. With the engine off and the key out, inspect the throttle body for carbon buildup. On electronic throttles, don't force the throttle plate open by hand; follow your vehicle's cleaning procedure, and don't turn the key on while your fingers are near the plate. After cleaning the throttle body or replacing parts, perform your vehicle's idle relearn procedure. Keep hands clear of the belts and fan when the engine is running.
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