BMW F20 118i engine trouble - Engine speed in neutral too high! (2000 rpm)

Here some problem of my 2016 BMW 118i Facelift model 136 hp which occurs from time to time.

Sometimes the rotational speed goes up to 2000 rpm while in neutral and then goes down below 1000 again. The car workshop cannot find the cause, told me it was the sparking plugs, but seems to continue after changing them. Motor sounds weird in neutral. Fault memory says that "mixture extremely too lean"

Any experience with that somebody?

Видео BMW F20 118i engine trouble - Engine speed in neutral too high! (2000 rpm) канала Lou FRN