P0505 — Idle Air Control System Malfunction

P0505 means the idle control system can't hold target idle speed. A carboned-up throttle body or IAC valve is the most common cause and is often cleanable.

Cost range: $50–$500. Severity: medium. Safe to drive? Yes but the car may stall at stops, which matters in traffic.

Most common causes of P0505

1. Carbon buildup in throttle body or IAC passage — Cleaning fixes a large share of these. Relearn idle afterwards. ($50–$180)
2. Failed idle air control valve — On older vehicles with a separate IAC motor. ($120–$400)
3. Vacuum leak — Unmetered air overrides idle control authority. ($50–$300)
4. Failed electronic throttle body — On drive-by-wire vehicles. ($300–$700)

Symptoms drivers report with P0505

• Idle too high or too low
• Stalling at stops
• Surging idle
• Hard restart when warm