What are the reasons for the shaking during cold start of BMW 5 Series?
2 Answers
The reasons for the shaking during cold start of BMW 5 Series are: 1. Excessive carbon deposits inside the engine, leading to an overly lean air-fuel mixture during cold start, causing shaking; 2. Mechanical failures such as ignition coils, spark plugs, or fuel injectors; 3. Low oil pressure or cylinder pressure, resulting in insufficient power; 4. Poor fuel quality; 5. Damaged or excessively dirty idle control valve; 6. Intake manifold leakage; 7. Damaged engine mounts or rubber pads; 8. Oxidized or low-grade engine oil. Taking the 2021 BMW 525li as an example, it is a mid-to-large-sized 4-door 5-seater sedan with a body size of 5106mm in length, 1868mm in width, and 1500mm in height, with a wheelbase of 3105mm. This car is equipped with a 2.0T turbocharged engine and an 8-speed automatic transmission, delivering a maximum power of 135 kW and a maximum torque of 290 N·m.
Having driven a BMW 5 Series for seven or eight years, I've noticed that cold start shaking is quite common. The most common issue is carbon buildup, especially on the intake valves and throttle body. During cold starts, gasoline atomization is poor, and carbon deposits absorb fuel, leading to incorrect air-fuel mixture ratios. Another cause is aging spark plugs; after 30,000 to 40,000 kilometers, their ignition energy decreases, and the higher compression ratio during cold starts can cause shaking. Poor fuel quality can also have an impact, as clogged fuel injectors disrupt smooth fuel supply. A reminder to everyone: in winter, avoid turning on the heater immediately—give the engine a few dozen seconds to warm up. Regularly adding fuel system cleaner and driving at high speeds to clear carbon deposits is quite effective. If the shaking is severe, it's best to visit a shop for a computer diagnosis to check for sensor faults.
