Why does the engine shake at idle but stops shaking when accelerating?
2 Answers
The reasons why the engine shakes at idle but stops shaking when accelerating are: 1. Severe carbon buildup inside the engine: Carbon deposits on the throttle body, fuel injectors, spark plugs, and pistons. When these deposits accumulate to a certain extent, they absorb combustion heat, leading to conditions like pre-ignition or knocking; 2. Ignition system issues: Excessive carbon buildup on spark plugs or insufficient ignition voltage can cause misfiring, resulting in single or multiple cylinder misfires. This leads to insufficient engine power and thus shaking; 3. Unstable fuel pressure: The fuel system includes components like the fuel tank, fuel filter, fuel pump, oil-gas separator, fuel lines, and fuel gauge. A problem in any of these can cause unstable fuel pressure; 4. Aging of internal engine components: This typically occurs after the vehicle has been used for a certain number of years or miles. Severe loss of engine power can cause shaking, and such vehicles often shake at low RPMs, with symptoms improving somewhat after accelerating.
When it comes to idle shaking that stops when you step on the gas, I've encountered this situation frequently myself, especially in older cars. Generally speaking, this is mostly caused by engine instability at low RPMs—for example, excessive carbon buildup in the throttle body or clogged fuel injectors, which restrict air intake or fuel supply, making the engine struggle at idle. When you press the accelerator and the RPM increases, combustion improves, masking the issue. I've dealt with similar cases before—after cleaning the throttle body and intake tract and replacing the spark plugs, the problem improved significantly. Additionally, if the mass airflow sensor malfunctions or the ignition coil has cracks, it can also cause shaking, which becomes particularly noticeable at idle. For maintenance, I recommend using high-quality fuel and driving at highway speeds regularly to help clear carbon deposits and prevent minor issues from turning into major repairs. Don't ignore it—prolonged shaking increases engine stress and affects longevity. Spending a little on maintenance is worth it.
