P0305 BMW - on idle rpm fluctuate. after that it seem normal,

Question

1. Light service engine soon came on saturday , but went off sunday

Answer 1

If the problem went away it possible it was just a misfire that did not replicate and that is why the engine light went off.

if there light does not come on you should be fine, if you use low octane fuel that might cause the problem use 91 octane fuel from Shell or Chevron