What are the reasons for the engine speed dropping or even stalling when depressing the clutch?
2 Answers
The reasons for the engine speed dropping or even stalling when depressing the clutch include: incorrect driving operation and improper air-fuel ratio adjustment in the engine system. These reasons can lead to stalling. Incorrect driving operation: Releasing the clutch too quickly can cause the vehicle to shake, significantly increasing the likelihood of stalling. In such cases, it is necessary to release the clutch slowly or press the accelerator to increase power. Whether the clutch is released too quickly or too slowly, the vehicle may shake. At this point, pressing the accelerator is required to better match the engine speed with the vehicle's speed. Poor coordination can also result in stalling. Improper air-fuel ratio adjustment in the engine system: When the clutch is depressed, especially when transitioning from a no-load state to a load state, it can cause unstable engine speed. Common engine faults include poor performance in a certain cylinder, such as damage to the ignition coil or spark plugs; insufficient working pressure in the fuel system; excessive carbon buildup in the throttle, leading to sticking or inaccurate measurement of air intake. In such cases, a detailed inspection at a repair facility is necessary to further identify the cause of the fault.
I've driven manual transmission cars for over a decade and encountered this clutch-depress stalling issue several times. The main culprit is usually a faulty idle control system – either the idle air control valve gets carbon-clogged or fails, causing unstable engine RPM. Another possibility is intake system leaks, like aged/cracked vacuum hoses letting unmetered air disrupt the air-fuel ratio, which the ECU can't compensate for. Throttle body carbon buildup causing sticky throttle plates is also common, affecting airflow regulation. This issue is particularly annoying (and dangerous) when stalling at traffic lights. My advice: regularly clean these components during maintenance, replace vacuum hoses periodically, and use diagnostic scanners to troubleshoot – don't wait until you're stranded roadside.
