What are the causes of excessively high engine idle speed?

[CarsonAnn]

Engine idle speed being excessively high can be caused by: 1. Faults in the coolant temperature sensor, throttle position sensor, idle control valve, or fuel injector; 2. Throttle sticking or not closing properly; 3. Air leaks in the intake system. Solutions for excessively high engine idle speed include: 1. Cleaning or replacing the idle control valve and using a specialized decoder to perform a basic idle speed setting; 2. Cleaning and inspecting the fuel injector's spray volume to ensure there are no blockages or leaks; 3. Adjusting or replacing the throttle position sensor. The impacts of excessively high engine idle speed are: 1. Increased fuel consumption; 2. Damage to the clutch friction plate; 3. Increased vehicle noise.

[VanIsaac]

As an experienced driver, I've driven many cars and encountered high engine idle speed quite often. The most common causes are a dirty or stuck throttle valve that isn't moving smoothly, leading to air leaks in the intake pipe, or the idle control valve being clogged with sludge, disrupting air intake. Another issue could be a faulty idle speed sensor, which is supposed to regulate engine speed—if it malfunctions, the RPM fluctuates erratically. Additionally, problems in the ignition system, such as aging spark plugs, or leaking fuel injectors that disrupt the fuel mixture can cause the idle speed to spike. Ignoring this issue can lead to increased fuel consumption, excessive emissions, and even engine damage over time. It's recommended to check the throttle valve every six months and use high-quality engine oil as a preventive measure. In short, if you notice any problems, take your car to a professional repair shop as soon as possible—don't try to fix it yourself to save money, as safety should always come first.

[VonMariana]

When I helped a friend fix their car before, I encountered an issue with high idle speed, and the causes were varied. A malfunctioning throttle position sensor is a major problem—it sends incorrect signals to the ECU, causing erratic engine RPM. Air intake system leaks are also common, such as cracked or aged intake pipes allowing excess air in, making the engine rev excessively. A severely carbon-clogged idle control valve that gets stuck or a faulty coolant temperature sensor reporting incorrect high temperatures can also be culprits. If the fuel injectors have poor sealing and leak, disrupting the air-fuel mixture ratio, the idle speed may fluctuate unpredictably. Lastly, don’t overlook potential ECU malfunctions—if the central control unit fails, idle speed can spiral out of control. Regular cleaning of the intake system and using fuel system cleaners to keep components unobstructed can help prevent such issues. Proper maintenance ensures your car runs smoothly without tantrums.

[EthanRose]

Back when I was into car modifications, I often encountered high idle speed issues, which usually stemmed from minor components. A dirty throttle body with excessive carbon buildup restricts its opening and closing; the idle air control valve gets clogged or fails to operate; a faulty mass airflow sensor gives inaccurate readings; intake manifold leaks introduce extra airflow; and aging oxygen sensors provide incorrect feedback, leading to improper fuel injection. All these can cause the engine RPM to surge in neutral, wasting fuel and damaging the engine if not fixed promptly. Regular cleaning of these parts can help prevent such issues.