Is it normal for the engine to have intermittent idling vibrations but run smoothly?
3 Answers
Reasons for intermittent engine idling vibrations: fuel quality issues, severe engine carbon buildup. Specific explanations are as follows: Fuel quality issues: The function of fuel is to supply the engine with a certain amount of clean, well-atomized gasoline according to the operating conditions of the engine. If there is a problem with fuel quality, the quality of the gasoline will deteriorate. Therefore, the engine may experience vibrations, which can be resolved by switching to higher-quality fuel. Severe engine carbon buildup: Engine carbon buildup has always been a serious issue. It can be addressed by using higher-quality fuel or purchasing carbon removal products available on the market.
I just encountered this issue. The engine shakes like it's having spasms at idle, but it smooths out once I start driving. This is mostly due to aging spark plugs or failing ignition coils, causing uneven ignition and shaking. Excessive carbon buildup in the throttle body can also cause this—at idle, the air intake is low, and carbon deposits block the airflow, making it hard to breathe. Clogged fuel lines or unstable fuel injection from dirty injectors are especially noticeable at idle. Additionally, worn engine mounts with poor damping can amplify the shaking. Dirty sensors, like the oxygen sensor sending wrong signals, can confuse the ECU into adjusting the air-fuel mixture incorrectly, causing issues. You should check the spark plugs and carbon buildup immediately, and clean the throttle body. Otherwise, prolonged neglect will increase fuel consumption and damage the car.
My car had been idling so rough recently that I couldn't even keep my phone steady on it, but it ran fine while driving. The veteran mechanic said common causes include: ignition coil leakage causing intermittent misfires in a cylinder; inaccurate air-fuel ratio control by the ECU at idle; clogged fuel injectors causing uneven spray; carbon buildup having greater impact at low speeds. Additionally, exhaust valve leaks or stuck PCV valves may also cause shaking. Spark plugs tend to develop this issue after 60,000-70,000 km and should be checked. Quick diagnostic method: if shaking reduces when shifted to Neutral, it's likely due to failed engine mounts. Have the issue properly diagnosed during maintenance - don't wait until it develops into starting difficulties.
