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Symptom

Idle stays high when the engine is warm

The engine sits at fifteen hundred or two thousand revs at a standstill and will not come down, long after the warm-up period when a fast idle is normal and expected. Distinct from an idle that hunts or surges, which wanders about a target; this one holds steady at the wrong number, and that difference points at a different half of the system — something letting air past when it should not, rather than something failing to control the air it has. Worth noting whether the idle drops when you blip the throttle, and whether it also stays high with the air conditioning off.

Also described as: idle too high, high idle, revs stay high, idles fast, engine wont idle down, fast idle when warm, دور موتور بالا میماند, دور ارام زیاد است, ralenti alto en caliente, revoluciones altas en caliente, ralenti muy alto, marcha minima alta, الرلنتي عالي على الساخن, دورات عالية والمحرك حامي, الرلنتي مرتفع

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What this usually means

An idle that holds steady at the wrong number is a different fault from one that hunts, and the corpus keeps them apart deliberately. Hunting means the control cannot settle. Holding high means the control is settled — at a speed it should not be at, which usually means air is getting in that the module is not accounting for, or the module believes a condition that is not true.

The commonest cause is unmetered air, and at a warm idle the effect is at its most visible because the throttle is nearly closed and any leak is a large fraction of total airflow. The management sees more air than it commanded, fuels for it, and the engine settles at a higher speed. The tell is that blipping the throttle does not bring it down — it returns to the same elevated speed, because nothing about the leak has changed.

A throttle plate not returning fully does the same thing mechanically, whether from carbon around its edge, a sticking linkage on an older car, or a floor mat fouling the pedal. So does an adaptation that no longer matches the hardware after a clean or a battery disconnection.

And a large group is not a fault at all. A fast idle is correct while the engine is warming, when the air conditioning compressor is running, when the alternator is under heavy load, on some cars during a particulate filter regeneration, and often when the battery is being recharged after a low state of charge. Ask what the car is doing before diagnosing it — and specifically whether the idle is also high with the air conditioning switched off, which the vocabulary description already flags as the question worth asking.

Working through it

  • Holds high, blipping the throttle does not bring it down

    Likely cause
    Unmetered air entering downstream of the throttle — a hose, gasket, servo diaphragm or crankcase ventilation path
    How to confirm it
    Smoke-test the induction including the brake servo hose. Lean trims at idle that normalise at cruise corroborate it.
    What fixes it
    Renew the leaking hose or gasket. Re-check afterwards; a second leak is common once one is found.

  • Idle high with the throttle plate not seating fully

    Likely cause
    Carbon around the plate, a sticking linkage, or something fouling the pedal
    How to confirm it
    Inspect the bore and plate edge with the hose off; check the pedal travels freely and that no mat is fouling it.
    What fixes it
    Clean the throttle body and re-learn the adaptation. Free or renew the linkage where it sticks.

  • Began after a throttle clean or a battery disconnection

    Likely cause
    Adaptation lost or never re-learned — the module is working from values that do not match the hardware
    How to confirm it
    Ask what was done. Compare live closed-throttle position against specification before ordering anything.
    What fixes it
    Run the manufacturer's adaptation procedure. No part is required.

  • High only with the air conditioning on, or with heavy electrical load

    Likely cause
    Not a fault — the idle is raised deliberately to carry the compressor or the alternator load
    How to confirm it
    Switch each load off in turn and compare. This is the question the vocabulary description already asks and it resolves a good share of these complaints.
    What fixes it
    No repair. Explain rather than diagnose.

  • High for a sustained period on a diesel, with a warm exhaust smell

    Likely cause
    A particulate filter regeneration in progress — engine speed is raised deliberately to reach the required temperature
    How to confirm it
    Read regeneration status live. It ends by itself, which is the discrimination from a fault.
    What fixes it
    No repair, unless regenerations are unusually frequent — in which case diagnose that instead.

  • Idle stays high with a coolant temperature reading below normal

    Likely cause
    The management still believes the engine is warming up — a temperature sensor reading cold, or a thermostat stuck open
    How to confirm it
    Compare live coolant temperature against the operating figure on a long run, and against the heater's actual output.
    What fixes it
    Renew the sensor or the thermostat. The fast idle is correct behaviour for the temperature the module is being told.

Codes that produce this symptom (3)

Listed with the codes that most typically present this way first — the likeliest place to start.

Information, not instruction

CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.

Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.

Others with this symptom

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What makes one worth reading:

  • The car — make, model, year and engine. The same fault behaves differently on each.
  • What you measured, not only what you replaced.
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