What are the effects of revving the engine in neutral gear?

[SanWeston]

Revving the engine in neutral gear can have the following consequences: 1. Incomplete combustion. 2. Carbon buildup. 3. Clogging of the three-way catalytic converter. The working principle of the throttle: When the accelerator pedal is pressed, it directly controls the throttle valve, causing the throttle opening to increase and allowing more air to enter the engine. At this point, the ECU commands the fuel injection system to inject more fuel, increasing the engine speed and accelerating the vehicle. Precautions for pressing the accelerator pedal include: 1. Press and release the accelerator pedal gently and smoothly. 2. Coordinate the release of the clutch with pressing the accelerator pedal promptly and precisely. 3. Select the appropriate gear to ensure the engine operates mostly at medium speed and with a larger throttle opening to save fuel. 4. Before driving or turning off the engine, release the accelerator pedal first and avoid revving the engine in neutral gear abruptly.

[AshleyFitz]

I often see car owners revving the engine aggressively in neutral while waiting at red lights. There's really no need to put the car through such abuse. When the engine revs at high speeds without load, the piston movement accelerates drastically but lacks corresponding resistance, which can cause abnormal wear on piston rings and cylinder walls. In severe cases, it may even lead to cylinder scoring. Moreover, high RPMs in neutral increase fuel injection, resulting in fuel consumption 2-3 times higher than normal driving. Unburned gasoline can also form carbon deposits on the back of the valves. Last time, my neighbor's Civic had abnormal engine noise, and upon disassembly, it was found that the connecting rod bearings had worn grooves. The mechanic said it was caused by frequently revving the engine in neutral. This is a common sight in repair shops. If you need to warm up the engine during a cold start, maintaining 30 seconds of idling is sufficient—revving the engine only harms its lifespan.

[CaydenMarie]

As a mechanic, I have to talk about the dangers of revving the engine in neutral. When the engine suddenly revs up to 5,000 or 6,000 RPM, the crankshaft speed surges instantly but the transmission doesn't transfer power. This violent change subjects the flywheel to impact. Although the oil pump increases oil supply, the oil film on the crankshaft connecting rod bearings can easily rupture under high pressure, potentially causing bearing wear over time. More seriously, with the throttle fully open but abnormal intake manifold pressure, the ECU may incorrectly adjust the air-fuel ratio, leading to oxygen sensor poisoning. Last week, I worked on an old Excelle that had developed a habit of revving in neutral—the result was a melted and clogged catalytic converter from excessive heat, costing nearly 2,000 yuan in repairs. Actually, when waiting at a red light for more than 20 seconds, the start-stop system kicks in, making it completely unnecessary to deliberately rev the engine.

[RemingtonAnn]

Revving in neutral directly hits your wallet. Fuel consumption tests show: a 2.0L engine revved to 4000 rpm in neutral burns 60ml of gasoline per minute, equivalent to the fuel used for 3km of normal driving. Emission tests reveal HC (hydrocarbons) levels spike 5 times higher—wasting money and polluting. Mechanically, in automatic transmissions, the torque converter's turbine spins freely in neutral, causing transmission fluid to overheat abnormally beyond 120°C, accelerating fluid oxidation. Some believe this clears carbon deposits, but high RPMs actually stir up sludge from the oil pan, clogging oil passages. The worst case witnessed was CVT chain slippage due to prolonged neutral high-revving causing abnormal oil pressure.