What Causes Sudden RPM Increase in Neutral Gear?

[AnnaLynn]

Sudden RPM increase in neutral gear may be caused by slight throttle sticking. Below is relevant information about automotive transmissions: 1. Functions: (1) Change transmission ratio to expand the variation range of driving wheel torque and speed, adapting to frequently changing driving conditions while keeping the engine operating under favorable conditions; (2) Utilize neutral gear to interrupt power transmission, allowing engine startup, idling, and facilitating gear shifting or power output. 2. Components: (1) Housing: Used to install and support all transmission components and store lubricating oil. The housing should have sufficient rigidity with reinforced inner walls, featuring complex shapes and mostly being castings; (2) Transmission components: Refer to gears, shafts, bearings and other transmission parts. Shaft dimensions are determined through strength and stiffness calculations, primarily depending on stiffness. Since carbon steel and alloy steel have nearly equal elastic modulus, carbon steel is generally used. Alloy steel is only employed when gears and shafts are integrated or when shaft loads are severe.

[Peggy]

Last time I was driving in neutral, the engine RPM suddenly surged, which really startled me. This is usually related to the idle control system, like that small idle motor getting stuck and failing to regulate the speed properly, or a dirty air filter affecting the air intake. A cracked vacuum tube leaking air can also cause the engine to think it needs to work harder. Sensor issues are common too, such as the throttle position sensor reading incorrect data and sending wrong commands to the ECU. If the electronic control unit has a bug, it can directly cause unstable RPM. Not to mention that one time I encountered a stuck accelerator pedal causing high RPM—fortunately, I noticed it in time to avoid major repairs. In short, don’t underestimate this issue; it can waste fuel and even lead to sudden stalling, posing safety risks. I recommend not trying to fix it yourself—get it checked at a professional shop first to ensure the wiring and sensors are functioning properly.

[OOscar]

I've experienced several instances of high idle speed while commuting, which feels both annoying and dangerous. This is mostly caused by vacuum leaks sucking in excess air, making the engine think the load has increased, or the idle control valve being clogged with sludge and unable to maintain a stable speed. Other possibilities include a faulty coolant temperature sensor misleading the ECU into raising idle speed when the engine is cold, or even an ECU software bug randomly increasing the RPM. Some modified cars are more prone to this issue due to improper tuning. Prolonged high idle not only leads to a surge in fuel consumption but may also cause carbon buildup and damage internal engine components. A friend of mine ignored it and ended up stranded on the road. So, I believe if you notice unexplained RPM surges, immediately turn off the AC to reduce load, pull over safely, check vacuum hoses for cracks, and tow to a repair shop if necessary.

[LeCole]

As a car enthusiast, I know that high idle RPM is often a sign of unstable idling. I've tried checking for air leaks in the intake pipes by listening for hissing sounds, and whether the throttle position sensor is sticking and needs cleaning with some spray cleaner. Sometimes it's simply too much carbon buildup jamming the idle air control valve and disrupting airflow. If the RPM stays high, don't rush to drive to avoid damaging the oxygen sensor and catalytic converter, which would increase repair costs. I once solved the problem by spending just a few dozen dollars to replace the idle air control valve, which was much more cost-effective than a major overhaul. Regular carbon cleaning and maintenance are essential to keep the idle smooth.

[StBennett]

As the primary family car, I prioritize safety and economy. A sudden increase in idle speed indicates potential faults, such as aging idle control units with slow response or the computer receiving incorrect throttle signals, mistakenly increasing the RPM. This not only raises the risk of accidents, like losing control and crashing, but also wastes gasoline unnecessarily, causing monthly expenses to skyrocket. Especially on highways, it could lead to accidents, compromising children's safety. Common causes include air intake system leaks or sensor short circuits, requiring professional tools for diagnosis. I make it a habit to regularly maintain and clean the throttle body to prevent minor issues from escalating into costly repairs.