P0518: Idle Air Control Circuit Intermittent (Meaning, Causes, Fixes)
What P0518 means
At idle the throttle plate is nearly closed, so the engine needs a controlled extra air path to keep running. On many vehicles that path is an idle air control (IAC) valve on or near the throttle body, which the powertrain control module (PCM) opens and closes constantly to hold the target idle speed. OBD-Codes.com says P0518 is stored when the PCM detects an intermittent problem with the IAC circuit, and engine RPM fails to match the programmed limits; any other, more specific IAC codes should be diagnosed and repaired first. RepairPal describes it more simply: the PCM can't achieve the desired idle RPM. It is a generic OBD-II code that OBD-Codes.com says applies to 1996 and newer vehicles, including Dodge, Chrysler, Hyundai, Jeep and Mazda. The word intermittent matters: the fault comes and goes, so a loose connector or chafed wire that only loses contact some of the time is a typical suspect, and OBD-Codes.com suggests writing down the freeze frame data before clearing the code.
Severity: can I keep driving?
Stop and fix promptly
Both sources treat this as serious. OBD-Codes.com says P0518 should be treated as severe and addressed with urgency because the engine may stall or idle at an unexpectedly high RPM, and RepairPal rates it Urgent, its highest level. Because the fault is intermittent, the car may run fine one day and stall at a stop the next, which can mean losing power assist for steering and brakes, so get it checked soon and be careful in traffic until then.
Common symptoms
- Check engine light on
- Engine idle speed higher than normal (both sources)
- Engine stalls, especially at idle or when coming to a stop (both sources)
- Unusual noises from the throttle body area (OBD-Codes.com)
- Other idle air control codes stored (OBD-Codes.com)
Likely causes
Roughly most to least common, based on the sources below. Your vehicle may differ.
- Defective idle air control motor or valve (both sources)
- Open or shorted IAC control wiring or connectors (OBD-Codes.com; RepairPal lists a wiring issue)
- Engine vacuum leak (OBD-Codes.com only)
- Carbon buildup in the throttle body or IAC valve (OBD-Codes.com only)
- Faulty PCM or a PCM programming error (both sources list the PCM)
Diagnostic steps you can do
Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.
- Read all stored codes and freeze frame data and write them down, since an intermittent code can be hard to catch again. OBD-Codes.com says to diagnose any other, more specific IAC codes first.
- Check for technical service bulletins (TSBs) and recalls for your vehicle, since there may be a known fix.
- Inspect the IAC wiring and connectors for damage, corrosion, loose pins or burnt spots and repair anything you find.
- Check for vacuum leaks, including the PCV valve and hoses, vacuum hoses, brake booster hose and check valve, a stuck-open EGR valve or leaking EGR gasket, and the intake manifold gasket.
- Clean carbon from the throttle body and IAC passages if your vehicle's procedure allows it.
- Clear the code and drive normally, letting the PCM complete its readiness checks, to see whether it returns.
Typical fixes
- Repair loose, corroded or damaged IAC wiring or connectors
- Repair any vacuum leak
- Clean carbon buildup from the throttle body or IAC valve
- Replace the idle air control valve if it fails the manufacturer's test
- Repair or reprogram the PCM (rare, only after other causes are ruled out)
Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.
🛠 When to call a pro
- The engine stalls in traffic or when stopping
- The fault comes and goes and you can't find a wiring problem (OBD-Codes.com recommends a scan tool, a digital volt/ohmmeter and a vehicle information source, and says to disconnect related controllers before testing circuit resistance)
- The idle stays very high and you need to test the IAC system (OBD-Codes.com describes removing the IAC valve to see whether the idle can be controlled, and testing the IAC motor against manufacturer specs)
- The code returns after wiring repairs, cleaning and a new valve
Where to buy
Plain search links. Always match parts to your exact year, make, model and engine.
FAQs
Is P0518 serious?
Yes. OBD-Codes.com says to treat it as severe and address it with urgency, and RepairPal rates it Urgent. Stalling at stops is the main risk, so get it fixed soon even if the car seems fine between episodes.
What is the most common cause of P0518?
Both sources list a failed idle air control valve, wiring problems and, less often, the PCM. OBD-Codes.com also lists vacuum leaks and carbon buildup in the throttle body or IAC valve. Because the code is intermittent, check connectors and wiring for loose or chafed spots carefully.
How is P0518 different from P0511 and P0519?
OBD-Codes.com titles P0511 Idle Air Control Circuit, P0518 Idle Air Control Circuit Intermittent, and P0519 Idle Air Control System Performance. P0518 points to a circuit fault that comes and goes, while P0519 is about how the whole system performs. More specific IAC codes should be fixed first.
Do the sources describe P0518 the same way?
Mostly. Both give the same name and rate it severe or Urgent. OBD-Codes.com describes an intermittent IAC circuit problem, while RepairPal only says the PCM can't achieve the desired idle RPM. Their cause lists also differ: OBD-Codes.com includes vacuum leaks, carbon buildup and a PCM programming error, which RepairPal doesn't list.
How much does it cost to fix P0518?
Neither source gives a repair cost. It depends on the cause, from cleaning a connector or fixing a vacuum hose to a throttle body cleaning or a new idle air control valve, so get the cause diagnosed first.
Sources
Last reviewed 2026-10-25. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.