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High Idle Speed

An idle speed higher than normal when warm usually means extra air is getting in, the throttle body is dirty or the idle has not been relearned.

Normal risk

Usually not urgent. An automatic car may creep more, so keep your foot on the brake.

Short answer · Why is my car idling high?

A high idle is normal for the first minutes after a cold start. If it stays high when warm, look for a vacuum leak, a dirty or sticking throttle body, or a missing idle relearn after battery or throttle work. A faulty coolant temperature sensor can also make the engine think it is cold.

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Safe checks you can do

  1. Wait for warm-upCold idle is higher on purpose.
  2. Listen for hissingVacuum leaks raise idle.
  3. Read the coolant temperatureIf it reads cold when warm, the sensor is suspect.

Questions that narrow it down

  1. High only when cold?Normal.
  2. Did it start after battery disconnection?Idle relearn needed.
  3. Does the rpm surge?Air leak or idle control.

Possible causes

Listed without ranking. Use the questions above to see which ones fit your car.

  1. Vacuum leakExtra air.
  2. Dirty throttle bodyWrong air at idle.
  3. Missing idle relearnAfter work on the throttle or battery.
  4. Coolant temperature sensor faultEngine thinks it is cold.

Questions about High Idle Speed

What is a normal idle speed?

It depends on the engine; many warm petrol engines idle around 600–900 rpm.

Is a high idle bad?

It wastes fuel and can make automatic cars creep, but is rarely harmful in itself.