OBD codes / P0505 / Honda Civic
P0505 on a Honda Civic
Idle Air Control System Malfunction
Older R18/D-series and pre-drive-by-wire K-series Civics with an IACV.
What P0505 usually means on a Civic
P0505 points to the Civic's idle control system not maintaining the commanded idle. On the older Civics that use an idle air control valve, a carbon-clogged IACV is the classic cause and produces a hunting or stalling idle. The valve sits on the throttle body and gums up over the years. Cleaning it resolves a large share of these.
Most likely causes on this model
- Carbon-clogged IACV
The idle air control valve cokes up on high-mileage Civics, causing surging or stalling and setting P0505.
- Dirty throttle body
Deposits around the throttle plate disturb idle airflow the ECU cannot correct.
- Vacuum leak affecting idle
An unmetered air leak makes the idle system run out of authority.
What it costs on a Civic
Cleaning the IACV and throttle body is nearly free if you do it yourself and inexpensive at a shop, and it fixes many P0505 Civics. A replacement IACV is a moderate part if cleaning does not hold. This is one of the cheaper idle-related repairs on the platform.
Year, engine and mileage change the answer. Get a diagnosis for your Civic — it weighs these causes against your exact configuration and real complaint data.
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Related symptoms
Honda Civic problems & recalls by year
Based on widely reported patterns for this model; individual causes vary by year, engine and history. Generic P0505 behavior is covered on the main P0505 page. Confirm with a scan tool before buying parts.