What conditions can cause abnormal noises in the engine at idle?

[KinsleyRose]

Excessive clearance, engine misfire, and engine knocking are all causes of abnormal noises in the engine at idle. The details are as follows: 1. Abnormal noise caused by excessive clearance. Clearance is an important factor in automotive assembly quality. When lubrication, temperature, load, and speed are constant, the abnormal noise becomes more noticeable as the clearance increases. Some engine components may produce abnormal noises due to wear-induced clearance enlargement. 2. Abnormal noise due to engine misfire. Engine misfire mainly refers to one or more cylinders not functioning properly, manifested by obvious intermittent exhaust gas flow and severe shaking of the exhaust pipe, accompanied by clear "popping" or thumping sounds from the engine.