What causes severe shaking when starting a cold BMW?
3 Answers
BMW experiences severe shaking when starting cold due to the following reasons: 1. Severe engine carbon buildup: When there is excessive 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, making it difficult to start and causing shaking. 2. Ignition system issues: Poor performance of the ignition system, such as spark plug misfiring, can lead to severe shaking when starting the car cold. 3. Unstable fuel pressure: Abnormal fuel pump supply pressure or incorrect readings and poor performance of the intake pressure sensor can cause body shaking. 4. Aging engine components: Worn-out components leading to engine mount issues can transmit vibrations to the steering wheel and cabin, causing shaking at idle.
I've been driving a BMW for several years, and cold start shaking is quite common, mostly caused by engine carbon deposits. Over time without cleaning, a lot of carbon accumulates inside the engine, especially during idle when fuel doesn't burn completely, leading to unstable air-fuel mixture and shaking during startup. Worn-out spark plugs or ignition coils are also a problem—when one cylinder misfires while others work, the car shakes like it's having a fit. In cold weather, engine oil becomes too thick with poor flow and insufficient lubrication, increasing engine load and making the shaking more noticeable. The intake system is another factor; for example, a dirty mass airflow sensor can cause incorrect air intake measurements. I used to clean the throttle body regularly and replace spark plugs, which significantly reduced the shaking—cost-effective and hassle-free. To prevent issues, I recommend using high-quality fuel and engine oil, along with an annual carbon cleaning.
Having driven for decades at my age, I know that BMW's cold start shaking is mostly due to wear and tear on small parts. The rubber in the engine mounts hardens over time, reducing shock absorption and causing severe jolts. Unstable spark plug ignition is also common; as they age, the ignition timing becomes inaccurate, leading to uncoordinated engine operation. I usually wait half a minute before starting in the morning to let the oil warm up and reduce friction. When there's a lot of carbon buildup, I drive more at low speeds since incomplete fuel combustion accumulates carbon deposits, and high-speed driving can burn some off. Clogged fuel injectors cause uneven gasoline spray, resulting in inconsistent air-fuel mixture and significant shaking. Faulty oxygen sensors misread data, leading to inaccurate fuel supply. I've experienced all these issues, and minor repairs or replacements usually fix them. Just avoid using low-quality fuel regularly.
