What Causes a BMW to Shake at Speeds Between 40-70?
2 Answers
BMW shaking at speeds between 40-70 can be attributed to the following reasons: Severe Engine Carbon Buildup: The most common cause of car shaking is a dirty throttle body or excessive carbon deposits in the fuel injectors. When there is too much carbon buildup inside the engine, the gasoline sprayed by the cold-start injector is largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts. This makes the engine difficult to start. In such cases, the engine only starts easily once the carbon deposits have absorbed enough gasoline to reach saturation. After starting, the gasoline adsorbed on the carbon deposits is then drawn into the combustion chamber by the engine's vacuum suction, causing the air-fuel mixture to become too rich. This fluctuation between lean and rich mixtures leads to idle shaking after a cold start. The lower the temperature, the more fuel is required for a cold start. Unstable Fuel Pressure: If you have already cleaned the engine carbon deposits, cleaned the throttle body, replaced the oil seals and spark plugs, but still notice the car shaking at idle, you should check whether the fuel supply pressure and the intake pressure sensor are functioning properly. Abnormal fuel pump pressure or incorrect readings and poor performance of the intake pressure sensor can also cause the car to shake.
When driving a BMW between 40 to 70 km/h and feeling severe shaking, it's usually caused by unbalanced tires or improper wheel alignment. I've driven a car with similar symptoms before - after changing tires without performing balancing and four-wheel alignment, the vehicle kept shaking at constant speeds, making the steering wheel tremble noticeably. Additionally, worn or damaged wheel bearings can also cause such vibrations, especially noticeable in medium speed ranges. Check if there's uneven tire wear or inconsistent tire pressure, as neglecting these minor issues can damage the suspension system over time and accelerate component wear. Regular vehicle maintenance, especially inspecting conditions before and after highway driving, can effectively prevent problems from worsening.
