What Causes the Engine Sound to Fluctuate Between Loud and Quiet During Hot Idle?
2 Answers
When the engine is idling while hot, the sound may fluctuate between loud and quiet, but as long as the variation is not very noticeable and there is no shaking, it is considered normal. Below is an introduction to car idling: Introduction to Car Idling: Idling is a working condition of the car, referring to the engine running in neutral. The engine speed during idling is called the idle speed. The idle speed can be adjusted by modifying the throttle size, among other factors. Idling means the engine is "producing power without doing work." When the engine is running, if the accelerator pedal is fully released, the engine enters the idle state. Causes of Unstable Idling: Direct causes refer to mechanical parts being dirty, worn, or incorrectly installed, leading to changes in cylinder power and resulting in an imbalance of power among the cylinders, causing unstable idling. Indirect causes refer to abnormalities in the engine's electronic control system, leading to poor combustion of the air-fuel mixture, making it difficult to balance the power among the cylinders and causing unstable idling.
My car often has fluctuating idle sounds after warming up, which could be caused by various factors. I think the most common issue is a problem with the ignition system, such as aging spark plugs or carbon buildup blocking them, leading to engine misfires. Alternatively, an unstable fuel pump supply or uneven gasoline injection can cause inconsistent combustion in the cylinders, naturally resulting in unstable sounds. I've encountered this a few times, mostly due to neglected regular maintenance. Additionally, a small valve or vacuum leak in the idle control system can disrupt RPM control, making the engine "breathe" unevenly. In short, this kind of problem shouldn't be delayed, as it can accelerate wear and even cause emission issues. I recommend first checking simple components, like replacing spark plugs or cleaning the throttle body. If that doesn't work, take it to a professional repair shop immediately to be safe. Using quality gasoline and regular maintenance can greatly reduce such troubles.
