Abnormal Noise from Car Muffler?

[DaisyFitz]

The causes of abnormal noise from a car muffler are as follows: 1. Leakage in the intake manifold or various valves. When the leakage affects the engine's vacuum, the engine will shake violently, especially impacting the idle speed when the engine is cold. 2. Excessive carbon buildup in the throttle and intake passages. Too much carbon and dirt in the throttle and surrounding intake passages change the cross-sectional area of the air passages, preventing the control unit from accurately controlling the idle air intake, resulting in an overly rich or lean mixture and abnormal combustion. 3. Faulty idle air control components. Malfunctions in the idle air control components lead to inaccurate idle air control. 4. Incorrect air intake. The control unit receives erroneous signals from the air flow sensor and issues incorrect commands, causing inaccurate idle air intake and abnormal mixture concentration, leading to abnormal engine combustion, which is an indirect cause of unstable idle speed.