P0511
Idle Air Control Circuit
Vehicle speed & idle control
Generic OBD-II
High
What it means
P0511 means the ECM has detected an electrical fault in the idle air control (IAC) circuit. The IAC valve meters air around the throttle plate to hold a steady idle. When its circuit fails, idle can run high, low, surge, or stall — and the engine may be hard to start. It's usually the IAC valve, its wiring, or carbon buildup; because stalling at stops is possible, treat it as a priority repair.
High
Can I keep driving? Maybe, but unreliably — the idle can surge, drop, or stall, so short careful trips only; a car that stalls at stops is a safety concern until fixed.
Common symptoms
What you'll notice
- Idle too high, too low, or surging
- Rough idle or stalling, especially at stops or when cold
- Hard starting or needing throttle to keep it running
- Check-engine light on
Common causes
Most likely first
- Faulty idle air control (IAC) valveLikely
- Open or short in the IAC circuit wiringCommon
- Corroded or loose IAC connectorCommon
- Carbon buildup in the IAC valve or throttle body/idle passageLess often
- Faulty ECM/PCM (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and note when the idle problem occurs (cold, warm, at stops).
- Inspect the IAC valve connector and wiring for opens, shorts, and corrosion.
- Remove and inspect the IAC valve; clean carbon from the valve and idle air passage.
- Test the IAC valve's resistance/operation against spec; replace it if faulty.
- If the valve and circuit are good, suspect the ECM driver. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0511?+
Use caution — the engine can stall at idle or stops, which is a safety risk. Keep trips short until the IAC circuit is repaired.
Can I just clear P0511?+
You can, but the idle problem and code return until the IAC valve or its wiring is repaired.
Related codes
Often seen with P0511
Read & clear P0511 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX