Is the throttle valve closed at idle?

[LaJake]

At idle, the throttle valve is not completely closed, leaving a very small gap that allows a minimal amount of air to flow through into the engine for combustion, thereby maintaining idle operation. Introduction to the throttle valve: The throttle valve is a controllable valve that regulates the entry of air into the engine. After entering the intake pipe, the air mixes with gasoline to form a combustible mixture, which then ignites to generate power. It connects the air filter at the top and the engine block at the bottom, often referred to as the "throat" of the automobile engine. Classification of throttle valves: Throttle valves are categorized into traditional cable-type and electronic throttle valves. In traditional engines, the throttle valve's operating mechanism works via a cable or linkage rod, connecting the accelerator pedal at one end and the throttle linkage plate at the other. Electronic throttle valves primarily use a throttle position sensor to adjust the throttle valve's opening angle based on the engine's energy requirements, thereby regulating the intake air volume.

[DelGenesis]

The throttle isn't completely closed at idle. Imagine the engine needs to breathe even at low speeds, so the throttle leaves a small gap for air intake. Older vehicles used idle speed control valves for adjustment, while modern electronic control systems directly regulate the throttle's slight opening to maintain airflow around 2.5 cubic meters per hour. Once after cleaning the throttle, my engine RPM fluctuated wildly because it was closed too tightly without sufficient gap. Electronic throttle systems automatically adjust the opening based on coolant temperature - during cold starts, the opening can reach up to 10%.

[MacBlakely]

During idle, the throttle valve actually remains slightly open, thanks to the return spring hidden inside the throttle body. The spring constantly pushes against the throttle plate to prevent it from fully closing, ensuring the engine has a breathing passage. For example, the Toyota 8AR engine maintains a throttle opening of about 1.5° at idle, with an air intake volume even less than that of a drinking straw. The ECU only issues the fuel injection command after detecting this minimal opening. Last time during a repair, I found a car enthusiast had adjusted the spring himself, causing the throttle to close too tightly, which resulted in the engine stalling directly.

[Dustin]

Strictly speaking, the throttle valve remains in a controlled open state during idle. The electronic control system precisely maintains an opening angle between 1-3°, equivalent to leaving a gap about the thickness of a pencil lead. This design meets minimum air intake requirements while reducing fuel consumption. The Volkswagen EA211 engine's air flow sensor displays 2.8g/s at idle, entirely sustained by that sub-millimeter gap. Don't believe online claims about removing the throttle body for manual closure during cleaning - such practices may cause unstable idle after reassembly.

[SanCatherine]

The throttle maintains an opening of about 2% at idle, just like a person slightly opening their mouth to breathe while sleeping. The ECU precisely controls the 14.7:1 air-fuel ratio through this narrow gap. You can see water dripping from the exhaust pipe, which is a sign of complete combustion. However, it's important to note that carbon buildup can cause the throttle to stick, leading to a deviation of 0.5° from the standard opening angle, which affects the air-fuel ratio. Modern Hyundai and Kia models use special coatings to reduce carbon buildup, and it's recommended to inspect them every 50,000 kilometers.

[McSilas]

I have disassembled and cleaned over a dozen types of throttle bodies, and can definitively say that they all exhibit slight opening at idle. Using a diagnostic scanner to read the data stream reveals the opening values: the BMW B48 engine shows 1.8° when cold and 1.2° when warm; the Mazda Skyactiv controls idle air intake at around 5kg/h. This slightly open state is more fuel-efficient than fully closed and also avoids frequent start-stop issues. Some people experience unstable idle after modifying to larger throttle bodies precisely because they disrupt the factory-calibrated balance of this slight opening.