OBD-II diagnostic trouble code
P0505Caution
Idle Control System Malfunction
The idle air control system regulates how much air bypasses the throttle plate at idle to keep engine speed steady. This general code means idle behavior is outside the expected range, without yet pinning down whether it's running too low or too high.
Symptoms
- Idle speed that hunts up and down instead of staying steady
- Engine occasionally stalls at stops, especially right after starting or when the AC kicks on
- Idle noticeably too high or too low compared to normal
- Rough or shaky idle
Likely causes
- Carbon buildup fouling the idle air control valve or throttle body — extremely common
- A vacuum leak affecting idle air balance
- Failed idle air control valve or electronic throttle body actuator
- Dirty or malfunctioning throttle position sensor feeding bad data to the idle control loop
How to diagnose it
- Inspect and clean the throttle body and idle air control valve — this alone resolves a large share of idle codes
- Check for vacuum leaks around the intake and throttle body gasket
- Test the idle air control valve's operation and the throttle position sensor's signal with a scan tool
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Code names are compiled from open/standardized SAE and ISO references. Explanations, symptoms, causes and fixes are original. Covers generic (P0/C0/B0/U0) codes only — manufacturer-specific codes are planned for a future update.
Frequently asked questions
Can I drive with P0505?
You can usually keep driving with P0505, but don't put it off — the underlying cause can get worse or lead to further damage the longer it goes unaddressed. Get it diagnosed as soon as you reasonably can.
How much does it cost to fix P0505?
Typical repair costs for {code} range from roughly 60 to 400 EUR, depending on the specific cause and your car — see the fixes listed above for a breakdown.
What causes P0505?
Carbon buildup fouling the idle air control valve or throttle body — extremely common A vacuum leak affecting idle air balance Failed idle air control valve or electronic throttle body actuator
Reviewed by Artyom SemenovAutomotive Editor · Fact-checked by Yauheni Kapliarchuk, Editor-in-Chief