P0505 on Toyota
Idle Air Control System Malfunction
P0505 on Toyota vehicles indicates idle air control system malfunction. Au7o has documented this code across 1 Toyota model — most commonly on 4Runner. P0505 indicates a malfunction in the idle air control (IAC) system, which manages how much air bypasses the throttle plate to keep the engine idling smoothly at the correct RPM. On older systems this is a dedicated IAC valve/motor; the computer uses it to raise idle for cold starts, A/C load, or accessory load. When the system can't maintain the target idle, you may get a high or low idle, surging, rough idle, or stalling — especially at stops or when cold. The cause is usually a dirty or failed IAC valve, but vacuum leaks and electrical faults are common too. Typical repair costs on Toyota range from $20 to $350, depending on the specific model and root cause.
Common Causes of P0505
- •Dirty or carbon-clogged idle air control valve
- •Failed IAC valve motor or stuck pintle
- •Vacuum leak in the intake system
- •Dirty throttle body or sticking throttle plate
- •Wiring or connector fault in the IAC circuit
- •Faulty PCV system causing unmetered air
- •PCM/ECM control fault
P0505 on Toyota by Model
Toyota 4Runner(1 issue)
- 3.4L 5VZ-FE Idle Air Control (IAC) Valve Carbon Fouling — Rough/Surging Idle, Stalling (P0505)1996-2002
The 3.4L 5VZ-FE uses a rotary-solenoid Idle Air Control (IAC) valve on the throttle body to manage idle. Over high mileage the IAC passages and valve clog with carbon and oil deposits, producing erratic idle (hunting between ~700 and ~1200 RPM), high idle, or low idle that shakes and stalls — often stalling at stops or when the A/C compressor loads the engine. It's a very frequent, well-documented maintenance item for 5VZ-FE 4Runners/Tacomas and commonly sets P0505 (idle control system malfunction).
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View P0505 across all makes →Frequently Asked Questions
What does P0505 mean on Toyota?▼
P0505 stands for "Idle Air Control System Malfunction." P0505 indicates a malfunction in the idle air control (IAC) system, which manages how much air bypasses the throttle plate to keep the engine idling smoothly at the correct RPM. On older systems this is a dedicated IAC valve/motor; the computer uses it to raise idle for cold starts, A/C load, or accessory load. When the system can't maintain the target idle, you may get a high or low idle, surging, rough idle, or stalling — especially at stops or when cold. The cause is usually a dirty or failed IAC valve, but vacuum leaks and electrical faults are common too. On Toyota specifically, this code is documented across 1 model.
What causes P0505 on Toyota vehicles?▼
Common causes on Toyota: Dirty or carbon-clogged idle air control valve, Failed IAC valve motor or stuck pintle, Vacuum leak in the intake system, Dirty throttle body or sticking throttle plate, Wiring or connector fault in the IAC circuit. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0505 on a Toyota?▼
Repair costs on Toyota range from $20 to $350, depending on the specific model and root cause.
Which Toyota models have P0505 documented?▼
Au7o has documented P0505 on 1 Toyota model: 4Runner.