Does High Idle Speed Consume More Fuel?
4 Answers
High idle speed consumes more fuel. During idle, the engine needs to be ready to respond to the driver's starting operation at any time. When starting the car, it transitions from a stationary to a moving state, requiring the engine to generate more torque than during normal driving. As a result, due to the inherent programming of the car's electronic fuel injection system, the fuel injector sprays slightly more fuel per cycle during idle compared to normal driving. Additionally, higher engine RPM leads to increased fuel consumption. Below are the effects of idle speed on car fuel consumption: 1. Introduction to idle fuel consumption: Small-displacement engines (e.g., MG5's 1.5L) may not necessarily have low idle fuel consumption, while large-displacement engines (e.g., Cadenza's 2.4L) may not necessarily have high idle fuel consumption. Turbocharged and direct-injection engines may have high idle fuel consumption (e.g., 1.4TSI) or low idle fuel consumption (e.g., A6L-30-FSI). 2. Idle fuel consumption labeling: Currently, idle fuel consumption is not a mandatory parameter listed in car specifications, though some manufacturers may include it in the manual.
Having driven for over twenty years, I can confirm that high idle speed does increase fuel consumption. Although the wheels aren't moving when the engine is idling, the fuel injectors keep spraying fuel continuously. Higher RPM means more fuel injection cycles per unit of time. Two years ago, my old Passat suddenly idled at 1200 RPM, and the fuel consumption jumped from 8 liters per 100 km to 11 liters. At the repair shop, we found it was caused by carbon buildup in the throttle body. After cleaning the throttle body, the idle speed dropped back to 750 RPM, and the fuel consumption immediately returned to normal. I recommend regularly checking the air filter and throttle body. If you notice unstable idle speed, don't delay repairs—fixing it early saves fuel. Also, it's best to turn off the engine when waiting parked for long periods. Otherwise, idling wastes fuel and promotes carbon buildup, which is neither eco-friendly nor cost-effective.
As a ride-hailing driver with three years of experience, I have a deep understanding of fuel consumption during idling. High idle speed definitely consumes more fuel because the higher the engine's RPM while idling, the more gasoline is burned. Especially in summer when the air conditioning is on, if the idle speed is slightly higher, you can visibly see the fuel gauge needle dropping. Last time, my car had a faulty idle control valve causing high idle speed, which increased fuel consumption by about 15%. Later, I developed a habit of shifting to neutral and pulling the handbrake when waiting at red lights for more than 30 seconds, which can reduce idle speed by about 200 RPM. Regularly maintaining proper tire pressure and changing engine oil also help control idle fuel consumption. The key is to address abnormal idle speed immediately—this not only saves fuel but also protects the engine.
Having worked in repair shops for over a decade, I've never seen a car with high idle speed that isn't fuel-thirsty. The principle is simple: increased RPM means the engine runs faster, fuel injectors work more frequently, naturally consuming more gasoline. Common causes include carbon buildup in the throttle body sticking, faulty coolant temperature sensor, vacuum line leaks, or damaged idle air control valve - all making the ECU miscalculate and increase fuel delivery. Just the other day, a Corolla's idle stubbornly stayed at 1000 RPM with 20% higher fuel consumption. We found the intake manifold gasket had aged and leaked. After replacement, idle stabilized at 750 RPM and fuel efficiency immediately returned to normal. I recommend cleaning the throttle body every 20,000 kilometers - it's quite effective for controlling idle fuel consumption.
