P0508 Code: Idle Air Control Circuit Low — Causes & Fix
P0508 means the idle air control (IAC) circuit signal is too low — the valve that meters idle air isn't being controlled correctly.
- Applies to
- All OBD-II vehicles (any make or model)
- Est. repair cost
- $30 – $400
- Time to fix
- 30 minutes – 2 hours
What it means
Causes include a carbon-clogged IAC valve, a short in the wiring, or a failed valve. P0508 is a generic OBD-II powertrain code defined in the SAE J2012 standard, so it applies to virtually any 1996-or-newer petrol car or light truck regardless of make. Fix the underlying fault, then clear the code with an OBD-II scan tool — it will return if the problem isn't resolved.
Symptoms
- Check engine light on
- Unstable idle or stalling
- Hard starting
How to fix it
- 1
Clean the IAC and throttle body
1. Clean carbon from the IAC valve and idle passages.
- 2
Inspect wiring / replace valve
1. Check the connector and wiring for a short. 2. Replace a failed IAC valve, then clear the code.
Frequently asked questions
Why does my car stall at idle with P0508?
A faulty or clogged idle air control valve can't hold the right idle air, so the engine stalls when the throttle closes. Cleaning or replacing it usually fixes it.
Last updated July 19, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.