OBD-II Code P0505 — What It Means & How to Fix It

What Does This Error Mean?

P0505 means your Idle Air Control (IAC) system is not functioning properly. The IAC valve controls how much air bypasses the throttle plate when your foot is off the gas. This is what keeps the engine running smoothly at idle. When it fails, the engine may idle too high, too low, or stall completely. You might notice the RPM bouncing up and down at stop lights.

Affected Models

All vehicles 1996+
Common in Nissan Altima and Sentra
Common in Honda Accord and Civic
Common in Toyota Corolla
Common in Chevrolet S-10 and Blazer

Common Causes

Idle air control valve is clogged with carbon buildup
IAC valve motor has failed electrically
Vacuum leak near the throttle body or intake manifold
Dirty throttle body restricting airflow at idle
Damaged or corroded wiring to the IAC valve

How to Fix It

Remove the IAC valve from the throttle body. It is usually held on by two or three bolts. Spray the valve and its port with throttle body cleaner to remove carbon buildup.

The IAC valve is typically located on or near the throttle body. It has an electrical connector with 2 to 4 wires.
While the IAC is off, clean the throttle body itself. Spray throttle body cleaner onto a rag and wipe the inside of the bore and the throttle plate. Remove all black carbon deposits.

Do not spray cleaner directly into the throttle body with the engine running. This can damage sensors.
Check for vacuum leaks around the intake manifold and throttle body. Spray carburetor cleaner around gaskets and hose connections with the engine running. A RPM change means you found a leak.

Common vacuum leak spots include the PCV valve hose, brake booster hose, and intake manifold gaskets.
Inspect the IAC valve wiring connector for corrosion or bent pins. Clean the connector with electrical contact cleaner. Make sure it clicks firmly when reconnected.

Corroded connector pins can cause intermittent idle problems that come and go.
Reinstall the IAC valve, clear the code, and let the engine idle for 5 to 10 minutes. The computer needs time to relearn the idle after cleaning. Do not touch the gas pedal during this relearn.

Some vehicles require a specific idle relearn procedure. Check your repair manual for your vehicle's process.

When to Call a Professional

If cleaning the IAC valve and throttle body does not resolve the issue, a professional can test the electrical circuit. A new IAC valve costs $50 to $200 depending on your vehicle. Labor is usually $50 to $150 since the valve is accessible. If the problem is a vacuum leak, diagnosis may take longer. Total repair at a shop typically costs $100 to $350.

Frequently Asked Questions

Why does my car stall at stop signs with P0505?

The IAC valve controls idle speed when your foot is off the gas. When it fails, the engine does not get enough air to maintain idle. This causes the RPM to drop too low and the engine stalls. It is especially noticeable when you come to a stop after driving.

Can I clean the IAC valve instead of replacing it?

Yes, cleaning works about half the time. Carbon buildup is the most common cause of IAC problems. Remove the valve and soak it in throttle body cleaner for 15 to 30 minutes. If cleaning does not fix the idle, the valve motor inside is likely burned out and needs replacement.

Do newer cars have IAC valves?

Most cars made after 2005 do not have a separate IAC valve. They use electronic throttle bodies that control idle speed directly. On these vehicles, P0505 may indicate a throttle body motor problem instead. The diagnostic approach is different for electronic throttle systems.