What is the reason for the start-up jitter of BMW n54 cold car?

The most common reason for the start-up jitter and flameout of BMW 5 Series cold car is carbon deposition. Carbon deposits generally appear in throttle valve, intake valve head, intake port, piston top and inner wall of combustion chamber. It is recommended that the owner go to the repair shop to find out the specific reasons and solve them as soon as possible, so as not to affect the use of the vehicle. Here's a brief introduction to car carbon deposit: (1) Too much carbon deposit on the inner wall of the throttle will cause insufficient air intake, difficult starting or easy flameout at idle speed. After the water temperature reaches the normal working temperature of the engine, the idle speed rises and falls due to the excessive opening of the throttle valve exceeding the normal idle speed, and the computer repeatedly adjusts the position of the throttle plate. (2) The surface of carbon deposit is loose and porous. When the cold car is started after parking for a night or a long time, most of the fuel injected by the injector begins to be absorbed by carbon deposits, and the fuel quantity in the cylinder is insufficient, so the mixture is thin and difficult to ignite. When the motor is running, the fuel injected into the cylinder for many times is enough to ignite. In this case, it will definitely be difficult to start. What's more, if there is too much carbon deposit in the head of the intake valve, the valve seal will be lax, and the cold start will be more difficult.