The engine sounds rough when idling or when the car is not moving and stopped this is because the engine cylinder is misfiring that results from a vacuum leak or a bad spark plug.
Possible Cause of Rough Engine Sounds on Idling
Engine Cylinder Misfiring
When the engine begins to sound rough when the engine is in idling condition, it only indicates that one or more of the engine cylinders is misfiring. The misfiring cylinders cause the engines natural balance, therefore, the sounds of the engine become rough.
Now, there is much possible cause of the engine cylinder to misfire. And all causes are not that easy to determine specifically without checking and testing of the actual engine.
However, there is the most common cause of cylinder misfire is a vacuum leak and bad spark plug or spark plug wires. If your car is equipped with the fuel injection system, it is possible that one of the fuel injectors is clogged. Clogged fuel injectors will starve the engine and the affected cylinder will misfire.
First thing you do is to replace both the spark plug and the spark plug wires. Usually, once both parts are replaced it will fix the engine rough sound on idling. But if the problem still occurs after replacing spark plug and spark plug wires then no other option but to bring the car to a car shop so that the engine will be tested to determine the cause of the rough engine sound, also mention to the mechanic what you have already done on the car so that the mechanic may diagnose the problem correctly.
See also: Engine Sounds Rough on Idling
