Idle Control System Malfunction
Engine · Idle Air Control
The idle speed control system is not maintaining proper idle RPM. You may notice rough idling, surging RPMs, or stalling when coming to a stop.
- Dirty or failed idle air control valveMost common
- Dirty throttle bodyMost common
- Vacuum leakCommon
Vehicles most commonly affected by P0505
Idle control system malfunctions are most commonly reported on Honda Accord and Civic (dirty IAC valves are a known maintenance item at 60,000-mile intervals), Nissan Altima with 2.5L QR25DE engines (carbon throttle body buildup), and Toyota Corolla and Camry with electronic throttle control systems. On drive-by-wire vehicles, P0505 indicates the throttle body needs cleaning rather than a separate IAC valve replacement.
Real-world P0505 diagnosis scenario
A 2006 Honda Accord 2.4L with 95,000 miles idles at 1,400 RPM (should be 700 RPM) and surges up and down at stoplights. P0505 and P0507 are both stored. The IAC (idle air control) valve is carbon-clogged — removing it and soaking in carburetor cleaner for 20 minutes followed by compressed air cleaning restores proper operation. Honda specifies a specific IAC cleaning procedure that requires also cleaning the IAC port in the throttle body. Total DIY cost: $8 for carburetor cleaner. Dealer cost for the same service: $150–$250.
On Honda 4-cylinder engines, P0505 is almost always a dirty IAC valve or throttle body — not a failed component. Always attempt cleaning before replacement. Honda's factory procedure calls for using a specific Honda cleaning product but any quality throttle body cleaner works. The key is also cleaning the bypass air port in the throttle body, not just the IAC valve itself.
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Frequently asked questions about P0505
What does P0505 mean?
The idle speed control system is not maintaining proper idle RPM. You may notice rough idling, surging RPMs, or stalling when coming to a stop.
Is P0505 serious?
Drive carefully — rough idle and stalling risk at stops.
How much does it cost to fix P0505?
Repair costs for P0505 range from $60 – $150 depending on the root cause and your vehicle.
Can I drive with P0505?
You can drive short distances but should have it repaired within 1–2 weeks to prevent further damage.
Is P0505 the same on drive-by-wire vehicles?
On newer drive-by-wire vehicles (most post-2005 engines), there is no separate IAC valve — the throttle body controls idle speed electronically. P0505 on these vehicles typically means the throttle body needs cleaning or the throttle position sensor has failed.
Can I drive with P0505?
Yes with caution — the car will typically drive but may idle roughly, stall at stops, or idle too high. Avoid high-traffic situations until repaired since stalling at intersections is a real possibility.
How much does throttle body cleaning cost?
DIY: $8–$15 for a can of throttle body cleaner. Shop service: $75–$150. This service is frequently recommended at 60,000-mile intervals on Honda and Toyota engines even without a code, as preventative maintenance.