BMW n20 engine started a little shaky after replacing the servo motor.

It should be the engine. I suggest you try another engine.

The intake control mechanism of BMW N20 engine mainly has two parts, one is electronic throttle, and the other is electronic valve stroke control mechanism. The introduction and adjustment of engine air volume is accomplished through the adjustable lift of intake valve, which is beneficial to reducing fuel consumption. The throttle is only used for emergency operation and starting. Under other working conditions, the throttle valve is fully open, and there is almost no throttling effect. Electronic valve technology can realize stepless adjustment of valve stroke and ensure the best balance of power and torque output at different engine speeds. In the full load position, the valve stroke and continuous opening time reach the peak, while in the idle position, they reach the lowest value.