How much does it cost to fix P0505 on a Honda?

Repair costs for P0505 on Honda vehicles typically range from $80 to $400 depending on the underlying cause. The most common fix is: Carbon buildup in the throttle body idle air passages restricting proper airflow control at idle..

Honda Check Engine Code

P0505 on Honda

Idle Air Control System Malfunction

Severity: medium DIY difficulty: 2/5 Honda cost: $80–$400

Last updated April 30, 2026 Also covers: Acura

P0505 on Honda: what makes it different

Honda's idle control system relies on a combination of the throttle body's idle air passages and the ECU's electronic idle control strategy, and on many Civic and Accord four-cylinder engines carbon buildup or a dirty/failing idle air control passage is the most frequent cause of rough or erratic idle codes.

Most-affected engines

K20/K24 (Civic, Accord, CR-V)
R18A 1.8L (Civic)
L15B7 1.5L turbo (Civic, CR-V)

Common model years: 2006–2019

Most likely cause on Honda

Carbon buildup in the throttle body idle air passages restricting proper airflow control at idle.

Known Honda engine-family issues

Honda's electronic throttle body design (used widely since the mid-2000s) is known to accumulate carbon deposits around the idle air passages over time, particularly on vehicles driven mostly in short trips or stop-and-go traffic, leading to rough or fluctuating idle before the code sets.

Honda-specific causes (most common first)

Carbon-fouled throttle body idle air control passages (very common on Honda four-cylinders)
Dirty or sticking throttle plate preventing the ECU from maintaining correct idle airflow
Vacuum leak at intake manifold gaskets or PCV hose connections
Failing electronic throttle body (ETC motor) losing precise control at low RPM
Dirty or clogged EGR passage affecting idle airflow calculations on applicable models
Low or contaminated engine coolant affecting idle air control temperature compensation

Honda-specific diagnostic tip

Before replacing any parts, remove the throttle body and inspect the idle air passages and throttle plate edges for carbon buildup — on Honda's electronic throttle body, a simple cleaning with throttle body cleaner and a soft brush often resolves the idle instability that triggers P0505.

Symptoms drivers report

Check engine light
High or low idle
Stalling at stops
Surging at idle

Typical repair cost on Honda

Most Honda owners fix P0505 for between $80 and $400, depending on which underlying cause turns out to be at fault. Start with the most-likely cause for your vehicle — Carbon buildup in the throttle body idle air passages restricting proper airflow control at idle. — before throwing parts at it.

Honda P0505 FAQ

Can I clean the throttle body myself to fix this on my Honda?

Yes, many Honda owners successfully resolve P0505 by removing the throttle body and manually cleaning carbon deposits from the bore and idle air passages with throttle body cleaner.

Will disconnecting the battery reset the idle after cleaning?

Yes, after cleaning the throttle body, disconnecting the battery for a few minutes or clearing the code lets the ECU relearn the idle baseline, which is often necessary on Honda's electronic throttle system.

Is P0505 related to the idle air control valve like on older cars?

Not exactly — most modern Hondas use an electronic throttle body instead of a separate idle air control valve, so the 'idle control system' in this code refers to the throttle body's idle air management rather than a standalone IAC valve.