P0507
- Powertrain
- Generic (SAE)
- Emissions
Diagnose soon
An elevated idle by itself is a driveability annoyance, not a mechanical emergency — the engine is not being damaged. Two things keep it above low. First, a high idle means the car pushes harder against the brakes at a stop and creeps more when you shift into gear, which is a real if minor control issue. Second, the most common cause is unmetered air, which leans out the mixture and, if the leak is large, can cause lean misfire and eventually catalyst damage. And one specific cause — a leaking brake booster diaphragm — is a braking concern that should be treated seriously on its own terms.
- Safe to drive
- Drivable, but expect a high idle that pushes against the brakes. Get it looked at soon; a leaking brake booster is urgent.
Idle Air Control System RPM Higher Than Expected
The engine is idling faster than the computer wants it to, and the computer has already closed the idle air passage as far as it can. Something is letting extra air into the engine that the computer doesn't control. Most of the time that is an air leak somewhere after the airflow sensor.
The ECU holds idle speed with a closed-loop strategy, metering a small controlled airflow around or through the throttle plate — via a stepper-type idle air control valve on older systems, or by commanding a small opening angle on an electronic throttle body on newer ones. P0507 sets when actual idle RPM exceeds the target while that air path is already commanded to its minimum position. The module has run out of downward authority. The extra air is entering through a path the ECU does not meter: a leak, a stuck-open valve elsewhere in the system, or a throttle plate that cannot fully close.
How the car detected itThe module compares measured engine speed against the calculated idle target — which itself varies with coolant temperature, transmission range, electrical load, and air conditioning demand — while the idle air control device sits at its minimum commanded position. When actual RPM exceeds target by more than a calibrated margin, commonly on the order of 100 to 200 RPM though the exact threshold is vehicle-specific, and stays there for a defined period, the fault is stored. Most calibrations require a warmed-up engine in closed loop with no other idle-up requests active.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Drivable, but expect a high idle that pushes against the brakes. Get it looked at soon; a leaking brake booster is urgent.
- Urgency
- Diagnose soon
- Will it pass emissions
- No
- If ignored
- Mostly you burn more fuel sitting still and live with a car that creeps at stops. The consequences that matter come from what is causing it. A sustained vacuum leak runs the engine lean, and long-term lean operation can cause misfire and overheat the catalytic converter. A stuck-open PCV path pulls crankcase vapour and oil mist into the intake, fouling the throttle body and intake valves. And if the source is the brake booster, the diaphragm is failing and pedal effort will increase, which is not something to defer.
- Check engine light
- Solid
- Clearing the light
- A completed drive cycle is normally required before the monitor re-runs and the light can clear.
- Idle speed too high, too low, or unstable
- Possible stalling at idle or after cold start
Many vehicles show no symptom at all beyond the warning light. The absence of a symptom does not mean the fault is not real.
These are the causes this code can have. For the order to work through them in, see what to check first.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | Vacuum leak bypassing IAC | Very common | — |
| 2 | PCV valve stuck open | Common | — |
| 3 | Brake booster diaphragm leaking | Common | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
In order. Each of these is cheaper or faster than what follows it, and each one can make the rest unnecessary.
Whether the throttle body was recently cleaned or replaced
On electronic throttle vehicles, cleaning the throttle body without performing the idle relearn is one of the most common causes of P0507. The module is still compensating for carbon that is no longer there. It costs nothing to fix and takes minutes.
Fuel trim values at idle compared with 2500 RPM
Positive short and long term trims at idle that fall back toward normal at higher RPM is the signature of unmetered air. This one comparison tells you whether to hunt for a leak or look elsewhere, before touching a single component.
The intake boot between the airflow sensor and the throttle body
Cracks on the underside of the accordion section are extremely common and hide from casual inspection. Any air entering after the MAF is unmeasured, and this is the most frequent single location.
The brake booster and its hose and check valve
It is a large vacuum consumer and a leaking diaphragm feeds a lot of unmetered air. More importantly, this is the one cause on the list that is also a braking problem, so it deserves ruling out early rather than late.
The PCV valve and its hoses, and the oil cap and dipstick seals
A stuck-open PCV valve or a cracked PCV hose is a direct unmetered air path, and these parts are cheap and easy to check. A missing dipstick seal or a loose oil cap can do the same thing.
Confirm actual versus target idle and the idle air command
Tools Scan tool with live data
With the engine warm and in closed loop, log commanded idle target, actual RPM, and either IAC step count or electronic throttle angle. Verify the target itself is sensible — a false cold reading from the coolant temperature sensor makes the module command a high idle legitimately, which is a different problem with the same symptom.
ExpectedActual idle matching the target, with the idle air device at a small nonzero position
Run the idle or throttle relearn if anything has been disturbed
Tools Scan tool with relearn function, factory procedure
Do this before paying for any diagnosis. If the throttle body has been cleaned or replaced, the throttle body or ECU changed, or the battery disconnected since the fault appeared, perform the manufacturer's relearn procedure now and re-check idle. It costs nothing, takes minutes, and it is the most common cause of this code. The procedure differs by manufacturer.
ExpectedIdle returns to target and the code does not reset
Read fuel trims at idle and at raised RPM
Tools Scan tool with live data
Record short and long term fuel trim at idle, then hold around 2000 to 2500 RPM and read them again. Strongly positive trim at idle that normalises at higher RPM points at unmetered air, because a fixed-size leak matters proportionally less as total airflow rises. Trim beyond roughly plus or minus 10 percent is worth investigating on any OBD-II vehicle.
ExpectedTrims within roughly plus or minus 10 percent at both idle and raised RPM
Smoke test the entire intake and vacuum system
Tools Smoke machine, regulated low-pressure supply, inspection light
This is the definitive test. Introduce smoke into the sealed intake tract downstream of the airflow sensor and watch for it escaping at the intake boot, throttle body gasket, intake manifold gaskets, injector seals, PCV hoses, brake booster hose, EVAP purge line, dipstick tube, and any vacuum-operated accessory. Use low pressure — the intake is not built to hold much.
ExpectedNo smoke escaping anywhere in the intake or vacuum system
Isolate the brake booster
Tools Soft-hose clamp or line plug, wheel chocks, scan tool
Clamp or plug the booster vacuum supply hose with the engine idling and watch whether the idle drops toward normal. Do this only with the vehicle stationary and in park with the wheels chocked, and restore the hose immediately afterwards — with the supply blocked the brake booster has no vacuum and pedal effort rises sharply, so never move or road-test the vehicle in this state. Clamp only soft rubber hose; plug, do not clamp, moulded plastic or hard nylon lines, which crack when squeezed and create a new leak. If the idle drops, the leak is in the booster, its hose, or the check valve. Treat a confirmed booster diaphragm leak as a brake system repair, not just an idle repair, and check pedal feel and reserve.
ExpectedNo change in idle speed when the booster is isolated
Isolate the PCV and EVAP purge paths
Tools Hose clamps, bidirectional scan tool
Clamp the PCV hose and the EVAP purge line one at a time and watch the idle — again only on soft rubber hose, and only with the vehicle stationary. A stuck-open purge valve is a frequently overlooked cause of unmetered air at idle — command it closed with a bidirectional scan tool and confirm it actually seals. A PCV valve should rattle when shaken and should not flow freely in both directions.
ExpectedIdle unchanged when each path is isolated, and the purge valve holding closed when commanded
Inspect the throttle plate, bore, and linkage
Tools Inspection light, approved throttle body cleaner, lint-free cloth
With the key off, look at the throttle plate seating. Carbon buildup at the edges holds the plate slightly open and is a leading cause on electronic throttle vehicles. On cable-operated systems, check for a binding cable, a sticky return spring, an over-tight cruise control cable, or a floor mat interfering with the pedal. Some throttle bores carry a coating that must not be scrubbed — the correct cleaning method varies by manufacturer.
ExpectedThrottle plate seating fully against a clean bore with free, fully returning linkage
Test the idle air control valve where one is fitted
Tools Bidirectional scan tool, multimeter, hand tools
On systems with a discrete IAC valve, remove it and check for carbon binding the pintle, then command it through its range with a bidirectional tool and confirm smooth full travel and a proper seat when closed. Check the valve's electrical circuit for opens and shorts. A valve that cannot close fully produces exactly this code.
ExpectedSmooth full travel with the pintle seating completely when commanded closed
Clean, relearn, and verify
Tools Scan tool with relearn function, factory procedure
After any throttle body cleaning, IAC replacement, or battery disconnection, perform the manufacturer's idle or throttle position relearn procedure again as the final step. Then let the engine reach full operating temperature, cycle the air conditioning and electrical loads, and confirm idle returns to target under each condition before calling it fixed. The relearn procedure differs by manufacturer.
ExpectedIdle settling at target across warm-up, air conditioning on, and electrical load
| Repair | Only after you confirm | Typical cost | Who |
|---|---|---|---|
| Perform the throttle body or idle relearn procedure | Throttle body was recently cleaned, replaced, or the battery disconnected, and idle returns to target after the relearn | $50–$150 | DIY |
| Replace a cracked intake boot, vacuum hose, or oil cap or dipstick seal | Smoke test shows the leak at that component and fuel trims normalise after replacement | $80–$380 | DIY |
| Replace the PCV valve or its hoses | Valve found stuck open or the hose cracked, with idle dropping toward target when the PCV path is clamped off | $80–$320 | DIY |
| Replace a stuck-open EVAP purge valve | Idle drops when the purge line is clamped, or the valve fails to seal when commanded closed with a bidirectional tool | $120–$380 | DIY |
| Clean the throttle body per the manufacturer's approved method and relearn | Carbon buildup visible around the throttle plate edges holding it off its seat | $100–$260 | DIY |
| Free or replace a binding throttle cable, return spring, or cruise control linkage | Throttle plate does not return fully to its stop with the pedal released | $80–$320 | DIY |
| Replace the idle air control valve | Valve fails to seat when commanded fully closed, or binds during a bidirectional sweep, with the intake proven leak-free | $150–$500 | DIY |
| Replace the throttle body | Throttle plate will not seat or the motor fails to hold the commanded minimum position after cleaning and relearn | $300–$950 | DIY |
| Replace intake manifold gaskets | Smoke test shows leakage at the manifold-to-head sealing surface | $250–$900 | Hard |
| Replace the brake booster, its hose, or the check valve | Idle drops toward target when the booster hose is clamped, and the booster fails to hold vacuum on test | $150–$1,100 | Hard |
Most P0507 repairs land at the cheap end — a hose, a PCV valve, a throttle body clean with a relearn. Do the relearn before paying for anything, since it is free and it is the most common cause. The genuinely useful spend after that is the smoke test, typically $80 to $150 as a diagnostic charge, because it turns a guessing game into a five-minute answer and usually pays for itself immediately. The high end of the range is reserved for intake manifold gaskets and brake boosters, both of which are labour-heavy. Ranges are US independent shop, parts plus labour.
- Cleaning the throttle body and skipping the relearn. This is the single most common way P0507 appears immediately after otherwise correct maintenance.
- Replacing the IAC valve because the code names the idle air control system. The code describes the symptom, not the cause, and a vacuum leak is far more likely than a failed valve.
- Not smoke testing. Small intake leaks are essentially impossible to find reliably by eye or by spraying flammable cleaner around a hot engine, and the spray method is genuinely a fire risk.
- Overlooking the EVAP purge valve. A purge valve that does not seal admits unmetered air and fuel vapour at idle, and it rarely gets checked because it is not thought of as an intake component.
- Scrubbing a coated throttle bore with abrasive cleaner. On several manufacturers this removes a factory coating and permanently changes idle airflow characteristics.
- Leaving the brake booster hose clamped or plugged after the isolation test, or driving the vehicle with it blocked. Pedal effort rises sharply with no vacuum at the booster.
- Clamping a plastic or hard nylon vacuum line instead of plugging it. The line cracks and you have created the leak you were looking for.
- Dismissing a leaking brake booster as merely an idle issue. The diaphragm is a brake system component and its failure affects pedal effort.
- Ignoring a false coolant temperature reading. If the ECU believes the engine is cold it will command a high idle correctly, and no amount of leak hunting will find a leak that isn't there.
- PCV Valve
- Intake Manifold
- Brake Booster
- Vacuum Hose
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Reviewed
Found something wrong? Tell us — we publish corrections.