What is the difference between high idle speed and low idle speed?
4 Answers
The difference between high idle speed and low idle speed lies in the different rotation speeds and fuel consumption. The following is a detailed introduction about the fuel consumption per 100 kilometers of a car: 1. Overview: The fuel consumption per 100 kilometers refers to the fuel consumption of a vehicle traveling a hundred kilometers on the road at a certain speed. It is a theoretical indicator of the vehicle. The fuel consumption per 100 kilometers is the value measured by the manufacturer in an objective environment using a dynamometer installed on the chassis of the vehicle, converted into speed parameters, and then specified speed driving is used to calculate the theoretical experimental fuel consumption data per 100 kilometers of the model. 2. Others: Since most vehicles are close to the economical speed at 90 kilometers per hour, most of the theoretical fuel consumption published externally is usually the fuel consumption per 100 kilometers at 90 kilometers per hour.
I've been driving for years and find the difference between high and low idle speeds quite noticeable. High idle means the engine revs too fast in neutral, like the tachometer needle soaring above 800 RPM, sounding like a loud hum as if the car's about to take off. Low idle is the opposite, with RPM dropping below 600, causing the car to shake violently and potentially stall when starting. This difference isn't just about RPM levels—it significantly impacts daily driving. High idle drastically increases fuel consumption and is noisy, while low idle makes it hard to start at traffic lights and can even prevent the engine from firing up. Common causes include a dirty throttle body, faulty sensors, or intake leaks. I recommend regular maintenance rather than waiting until problems escalate.
From a technical perspective, the main difference between high and low idle speeds lies in improper regulation by the engine control unit. High idle speed is often caused by erroneous signals received by the ECU, leading to excessive fuel injection and unstable RPM. Low idle speed is commonly due to insufficient air or spark plug carbon buildup, resulting in RPM drop and shaking. This affects fuel efficiency—high idle consumes more fuel, while low idle increases the risk of stalling and may even damage the catalytic converter. Based on my research of common vehicle models, the normal idle speed should be between 600-800 RPM. If abnormalities occur, using an OBD tool to read fault codes is the quickest solution; avoid manual adjustments.
As a novice driver with limited experience, I can clearly distinguish between high and low idle speeds. At high idle, the car roars loudly, feeling like a waste of gasoline; at low idle, the car seems powerless, frequently shaking and prone to stalling. This difference makes driving uncomfortable—high idle causes the car to rumble when stopping at intersections, while low idle makes it hard to control when starting from a red light. The cause might be dirty sensors or battery issues, which can be avoided with regular checks.
