Why is the idle speed high?
2 Answers
Here are the reasons for high idle fuel consumption: 1. The engine's throttle is dirty or malfunctioning. 2. The engine's spark plugs are faulty. 3. Excessive carbon deposits in the engine combustion chamber, intake tract, fuel injectors, or intake manifold lead to incomplete combustion. Below is an introduction to idle speed: 1. Idle state refers to a working 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. The reason idle speed increases fuel consumption is that the engine is operating in an abnormal state. 2. During idle, the engine speed is very low, intake turbulence weakens, and fuel atomization becomes poor, resulting in incomplete combustion. Additionally, prolonged fuel combustion time and increased cylinder heat dissipation losses also contribute to higher engine fuel consumption. 3. For naturally aspirated engines, the intake pressure is low and airflow is weak during idle, requiring the engine to inject more fuel to maintain higher fuel-air mixture concentration for operation, which also increases fuel consumption. Prolonged idling lowers engine temperature, slowing the evaporation of gasoline entering the valves, leading to carbon deposits.
As an experienced driver, I've seen too many cases of high idle speed issues, and 80% of the time it's due to sludge clogging the throttle body. The throttle body is like the throat of a car – when carbon buildup blocks the air intake, the ECU compensates by injecting more fuel to raise the RPM. My car had the same problem last time, and cleaning the throttle body immediately stabilized it. Also, don't underestimate those small rubber vacuum hoses – if they age and leak, the ECU detects abnormal air pressure and starts giving wrong commands. Another easily overlooked issue is a faulty coolant temperature sensor. Even when the engine is cold, it falsely reports adequate temperature, causing the ECU to incorrectly lower the RPM. If these problems aren't fixed promptly, not only will fuel consumption rise sharply, but carbon deposits will also accumulate worse. I recommend checking immediately when you notice unstable idle speed – don't let your engine suffer.
