What Causes Diesel Engine Idle Vibration That Disappears When Accelerating?
2 Answers
When accelerating, the engine's excitation frequency changes significantly, avoiding the natural frequency points of certain components in the drivetrain or vehicle body, thus eliminating vibration. Methods to diagnose idle vibration issues are as follows: 1. Assess the severity of vibration: Oxygen-deprivation-related vibrations typically exhibit large amplitudes. 2. Determine whether the idle vibration is irregular and intermittent. 3. Observe unstable idle RPM during vibration: If the tachometer needle fluctuates during idle, it indicates a problem. A properly functioning engine should exhibit uniform, minimal vibration with smooth operation when maintaining stable idle speed.
My diesel car keeps shaking when idling, but surprisingly becomes very stable when I step on the gas. After researching a lot, I found out this issue is quite common. It's mostly due to worn engine mounts—the deteriorated rubber pads can't buffer the slight vibrations at idle, while the engine runs more smoothly at higher speeds when accelerating. It might also be related to clogged fuel injectors causing uneven fuel spray at idle, leading to unstable cylinder operation, which improves as pressure increases when accelerating. I recommend checking the engine mounts and fuel system first, and trying high-quality diesel to prevent minor issues from escalating into safety hazards. Additionally, a dirty air filter affecting airflow can also cause problems at low RPMs—you can clean it yourself, but for a permanent fix, it's best to have a professional take a look.
