What are the reasons for high engine idle speed?

[LaSarah]

The reasons for high engine idle speed are: low temperature inside the cylinders and poor gasoline atomization. To meet the necessary combustion conditions, the electronic fuel injection system will require an increase in the concentration of the air-fuel mixture. As a result, the engine will raise the idle speed to increase fuel injection, thereby enhancing the concentration of the air-fuel mixture. Idle state refers to an operating condition when the engine is running without load. When the accelerator pedal is fully released while the engine is running, the engine enters idle state. During idle speed adjustment, the RPM should not fluctuate abruptly, as this can cause premature wear to the engine. An engine is a machine capable of converting other forms of energy into mechanical energy, including internal combustion engines, external combustion engines, jet engines, and electric motors.

[Reese]

I've seen many cases of high idle speed issues in cars, and there are quite a few possible causes. For example, carbon buildup in the throttle body can block it, preventing air from entering, and the ECU compensates by increasing the RPM. Dirty air flow meters giving inaccurate readings or stuck idle control valves are also very common. Vacuum leaks are another major factor because they allow extra air to enter, making the air-fuel mixture lean and disrupting idle control. Aging sensors like oxygen sensors or intake air temperature sensors malfunctioning can also mislead the ECU into incorrectly adjusting the idle speed. During diagnosis, using an OBD tool to read fault codes usually helps pinpoint the issue. Cleaning components yourself might provide temporary relief, but a professional fix is needed for a permanent solution. Prolonged high idle speed wastes fuel and damages the engine, so early detection and resolution are crucial.

[MiguelFitz]

I once encountered an idle speed as high as nearly 2000 RPM. At first, I thought it was normal for the engine to warm up in cold weather, but it remained high even after warming up. Upon inspection, it was found that the throttle body was completely dirty with black oil sludge. The mechanic said this is a common issue and cleaning it could bring the idle speed back to around 800 RPM. Aging and leaking vacuum hoses can also cause unstable idle speeds, just like my friend's car, where replacing the hose cost less than a hundred. If the idle speed control valve malfunctions, it can get stuck in one position, causing the RPM to remain constantly high. Don't underestimate high idle speeds; they can increase fuel consumption by more than 20% and make the exhaust smell foul. Regular maintenance is essential, and try to avoid parking in dusty areas to prevent component blockages.

[LaJulia]

High idle speed poses significant potential hazards, such as soaring fuel consumption wasting money, excessive emissions polluting the environment, and engine vibration when idling unstably, which can lead to severe wear or even component damage over time. Common causes include dirty or clogged throttle bodies, or vacuum tube cracks sucking in impurities. Sensor failures like malfunctioning air flow meters can also cause the system to misjudge RPM. Diagnosis is simple—just plug in an OBD scanner to read the data. Immediate repair is recommended to prevent minor issues from escalating, especially sudden malfunctions threatening safety during highway driving or in congested urban areas.