OBD codes / P0511
P0511
ModerateIdle Air Control Circuit
Drivable, with stalling as the main hazard — an engine that dies mid-turn takes the power steering and brake assist with it. If your car is stalling in traffic, fix this promptly; if it's just an unsteady idle, it can wait a short while but shouldn't be ignored.
What this code means
P0511 is the general-purpose electrical fault code for the idle air control circuit on older cable-throttle engines — the computer detected a problem in the IAC valve's circuit without narrowing it to specifically 'low' (P0508) or 'high' (P0509). The IAC valve is a small stepper motor or solenoid on the throttle body that bleeds air past the closed throttle plate to hold idle speed, and its circuit can fault from a failing valve, corroded connector pins, chafed wiring, or a poor ground. Carbon buildup is the classic underlying villain: gunked passages make the valve work harder and stick, which stresses the motor windings until they fail electrically. Symptoms are the familiar idle-control complaints — stalling at stops, a fast or hunting idle, and hard starts that need a foot on the gas. Diagnosis is straightforward: test the valve's windings, check power and ground at the connector, and clean the passages regardless of what you find.
Symptoms you might notice
- Stalling at idle, at stops, or on cold start
- Idle that hunts, surges, or sits too high or too low
- Hard starting unless you press the gas
- Idle dips when A/C or steering load comes on
- Check-engine light
What it costs to fix
Typical range: $30–$400 · about ~0.3–1 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| IAC valve and passage cleaning | $8–$20 | ~0.3–1 hrs |
| IAC valve replacement | $50–$250 | ~0.3–1 hrs |
| Wiring / connector repair | $5–$80 | ~0.5–1 hrs |
These are older-vehicle repairs with easy access, so costs stay modest. Cleaning is cheap and worth attempting first when the valve isn't electrically dead; if the windings test bad, replacement is the fix and cleaning the passages protects the new valve.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0511 for my exact vehicle →
Frequently asked
Can I just clean the IAC valve to fix P0511?
Often, yes — carbon buildup is the classic cause of IAC trouble, and cleaning the valve and its passages fixes many cases cheaply. But since P0511 is an electrical circuit code, test the valve's windings too: a valve that's electrically failed needs replacement, and cleaning alone won't bring it back.
Why does my car stall when I stop or put it in gear?
At closed throttle the IAC valve is the only thing feeding the engine air. When its circuit faults, the computer can't add air as load increases — so dropping into gear or turning the steering wheel drags idle down until the engine dies.
Does P0511 apply to newer drive-by-wire cars?
Generally no. Drive-by-wire engines control idle by moving the electronic throttle plate itself and have no separate IAC valve, so P0511 is overwhelmingly a code you'll see on older, cable-throttle vehicles.
How is P0511 different from P0505?
P0511 is an electrical fault in the IAC circuit — wiring, connector, or valve windings. P0505 is a broader idle-control-system malfunction that can set from mechanical problems like clogged passages or vacuum leaks even when the electrical circuit is fine.
Seeing P0511 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0511 for my vehicleRelated trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0511 from your phone — see our honest guide to the best OBD2 Bluetooth adapters.
Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.