What Causes Abnormal Noise When Releasing the Throttle in a Car?

[DelGabrielle]

It often occurs when there is insufficient torque. Most common abnormal noises in the engine depend on the engine's speed condition. 1. Causes of the noise: Excessive clearance between the piston and cylinder wall; Overly tight piston pin or connecting rod bearing assembly; Excessive clearance between the tappet and its guide hole; Wear on the camshaft profile; Sometimes, a loose starter clutch can cause the pulley to make noise (especially noticeable during speed changes). 2. Identification method: Many abnormal noises in the engine are clearly related to its load. During diagnosis, a method of gradually removing the load can be used for testing, typically employing single-cylinder or dual-cylinder misfire to remove the load from one or two cylinders, to determine the relationship between the noise and the load.