What Causes Sudden RPM Increase in Neutral Gear?
2 Answers
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.
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.
