What are the symptoms of unstable engine idle speed?
2 Answers
Unstable idle speed of a car engine mainly manifests in the following aspects: 1. The tachometer needle fluctuates up and down during idle, showing instability. 2. Vibration occurs during idle. The following are the reasons for unstable idle speed: 1. Clogged fuel injector: Leads to insufficient fuel supply pressure. Clogging of fuel injectors is usually caused by gum and carbon deposits in gasoline. 2. Faulty water temperature sensor: The car's water temperature sensor is generally installed on the engine block (or possibly on the water jacket of the cylinder head) and directly contacts the coolant (antifreeze) to measure the temperature of the engine coolant. Once the water temperature sensor fails, the car may experience unstable idle speed, difficulty starting when cold, inability to increase speed, and significantly increased fuel consumption. 3. Faulty throttle position sensor: The throttle position sensor detects whether the engine is in idle condition or under load operation, and whether the car is accelerating or decelerating. Damage to the throttle position sensor can cause engine vibration and unstable idle speed. 4. Air intake system leakage: The ECU controls the mixture concentration primarily based on intake air information such as water temperature, throttle opening, and engine speed provided by the air flow meter. Leakage in the intake air system can cause the ECU to inaccurately control the intake air volume, leading to unstable engine idle speed. 5. Exhaust system blockage: Causes poor exhaust, resulting in symptoms such as weak acceleration, reduced power, and unstable idle speed. 6. Weak spark from individual spark plugs: Leads to cylinder misfire, causing unstable engine idle speed, and may also result in black smoke from the exhaust pipe, reduced power, and backfiring.
When my car has unstable idling, the tachometer needle jumps up and down violently, as if it's dancing, especially noticeable when waiting at a red light or just after starting the engine. The entire car body shakes along, and I can feel the seat vibrating non-stop inside the car. Sometimes, I also hear the engine making gasping-like noises, like clattering or wheezing, which is really annoying. Over time, fuel consumption starts to rise sharply, and worse, the car is prone to suddenly stalling, such as during slow-speed following or at stop signs—it just dies as soon as I stop, forcing me to restart multiple times. I've also noticed that this issue is mostly caused by carbon buildup in the throttle body or clogged fuel injectors. Additionally, aging spark plugs can lead to uneven ignition, worsening the idle fluctuations. It's advisable to clean the engine components promptly to avoid developing more serious faults, saving both big repair costs and time.
