What Causes BMW Engine Shaking at Idle?
2 Answers
BMW engine shaking at idle is generally caused by severe carbon buildup in the engine, issues with the ignition system, or unstable fuel pressure. The specific reasons are analyzed as follows: 1. Severe engine carbon buildup: When there's excessive carbon deposit inside the engine, the gasoline injected by the cold-start fuel injector will be largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts and making ignition difficult. In this situation, the engine only starts easily after the carbon deposits become saturated with gasoline. After starting, the gasoline adsorbed on the carbon deposits will be drawn into the combustion chamber by the engine's vacuum suction and burned, making the air-fuel mixture too rich. This alternation between lean and rich mixtures causes idle shaking after cold starts. The lower the temperature, the more fuel is required for cold starts, and carbon deposits will significantly affect whether cold starts proceed smoothly. 2. Ignition system problems: Poor spark plug performance can also lead to such shaking phenomena. 3. Unstable fuel pressure: Abnormal fuel pump pressure or malfunctioning intake pressure sensors can both cause vehicle shaking.
Idle shaking is quite common in BMW vehicles. From my practical experience, it's usually related to the engine ignition system, possibly caused by aging spark plugs. Worn spark plug electrodes lead to incomplete ignition, causing the engine to misfire and shake; or there might be cracks in the ignition coils, with unstable high-voltage line transmission causing significant vibration. Fuel system issues can also contribute, such as slightly clogged fuel injectors or insufficient fuel pump pressure making the air-fuel mixture uneven, which becomes apparent at idle. Carbon buildup is particularly severe, often resulting from long-term short-distance driving without highway speeds. For a simple check, you can start by replacing the spark plugs. If there's no improvement, then clean the throttle body. Ignoring the issue may lead to higher fuel consumption and, over time, damage the engine's lifespan. BMW engines are precision-engineered, so proper maintenance is crucial. Regular servicing can prevent most problems.
