Why does a BMW shake when starting a hot car?

[WilliamLynn]

BMW hot car start shaking reasons are as follows: Too low temperature: Mainly due to the too low temperature, the lubricating oil is in a semi-solidified state and cannot fully start the lubrication, so the resistance during the starting process is greater than that when starting at normal temperature, thus causing the shaking phenomenon. The car has been parked for a long time: The oil in the engine flows back to the oil pan at the bottom of the engine. Therefore, after not using the car for a long time (such as overnight), when starting the engine, the upper part of the engine is actually in a state without oil and lacks lubrication. It takes about 30 seconds after starting before the oil pump operates to deliver oil to the parts of the engine that need lubrication the most, such as the pistons, connecting rods, and crankshaft.

[McConnor]

I've been driving a BMW for several years, and engine shaking during hot starts is quite common. It's usually caused by issues in the ignition system, such as worn-out spark plugs or faulty ignition coils, which make the engine run unevenly and shake. BMW's ignition coils are prone to failure under high temperatures, leading to incomplete combustion of the air-fuel mixture. The fuel system is also related—clogged fuel injectors or unstable fuel pressure can cause shaking. Additionally, if the engine mounts are loose or worn, they won't provide enough cushioning during startup, resulting in noticeable body vibrations. Carbon buildup in the throttle body or intake manifold may not cause issues at low temperatures, but during hot starts, abnormal airflow can trigger shaking. These problems are frequent in BMW's N52 or N55 engines. Once, I checked the spark plugs myself and found them eroded—replacing them fixed the issue. I recommend first inspecting the spark plugs and ignition coils, regularly cleaning carbon deposits, and using high-quality fuel as a preventive measure. If the shaking is severe, get it repaired early to avoid chain reactions damaging other components.

[JulianAnn]

My BMW used to shake even during warm starts. I suspected it was time to change the spark plugs, and upon opening them myself, I found them blackened and cracked. After replacement, it became much smoother. A dirty air filter also affects performance by restricting airflow, making the engine 'starve' and exacerbating shaking during hot starts. Then there are the engine mounts – when the rubber cushions age and loosen, the initial start-up vibration can shake the seats. A clogged fuel filter or malfunctioning injectors causing insufficient fuel supply also leads to shaking. I make it a habit to have the mechanic check these parts during every service to avoid sudden issues. Though minor, shaking is annoying; fixing it promptly ensures a comfortable and fuel-efficient ride. With BMWs, regular checks are essential.

[SadieDella]

Encountering hot start shaking, safety first and don't take it lightly. Continuous shaking may lead to stalling on the road, posing dangers. I suggest stopping immediately and not forcing it to drive. BMW sensors like the crankshaft position sensor failure can misreport data during hot starts, causing the engine control to malfunction and shake. High temperatures can vaporize and block the fuel lines, hindering the fuel pump and leading to unstable fuel supply and vibrations. When the oxygen sensor is abnormal, it provides incorrect feedback, causing mixture ratio imbalance and triggering issues. In these cases, promptly using a fault code reader for detection helps locate the problem. If not repaired, prolonged shaking can worsen fuel consumption or damage the engine. For driving safety, seek professional repair quickly if shaking is noticeable.