Why Does the RPM Increase When Pressing the Clutch in a Manual Transmission Car?
2 Answers
Manual transmission cars experience an increase in RPM when the clutch is pressed due to the following reasons: Fast Clutch Press and Slow Throttle Release: Normally, when shifting gears, the clutch is pressed while the throttle is released simultaneously. At the moment the power is cut off, the engine RPM begins to drop. If the throttle is released too early, the engine RPM drops first, which may cause engine braking and result in a jerking sensation, as if suddenly hitting the brakes. If the throttle is released too late, the clutch is already disengaged, and pressing the throttle while the engine is under no load will inevitably cause the RPM to rise. Idling While Driving: In traffic jams, when driving in first gear without pressing the throttle and relying on idle speed to move forward, the idle switch in the throttle body is engaged. The ECU controls the engine operation under idle conditions, maintaining the RPM at the target idle speed. Since the vehicle is in motion, the idle speed will be slightly higher, which is the ECU's idle compensation function. If the RPM increases beyond the target idle speed, the ECU will intervene to restore the idle speed to the target level for the current driving condition.
I've been driving a manual transmission car for several years and noticed that the RPM occasionally rises when I press the clutch. This usually isn't a major issue but rather a minor adjustment by the engine after a sudden reduction in load. Think of it this way: pressing the clutch separates the wheels from the engine, making the engine suddenly free of load. The computer control will automatically add a bit of fuel to prevent stalling, maintaining stability like during idle. If the RPM rises excessively, say from 1000 to 2000, it might indicate clogged fuel lines or a dirty idle control valve, which could wear out parts over time. It's advisable to use good-quality fuel and clean the throttle body regularly. If it happens frequently, have a mechanic check the sensors or if the throttle pedal is sticking. Don't panic unnecessarily, but stay alert for safety.
