You could try changing the oil (take something cheaper as flush, not Motul, filter change optional, save €),then drive few hundred kilometers on it, but not all on short distances so that the engine reaches and stays on operating temperature as much as possible, and then change the oil again with filter this time. This should flush the engine nonaggressively. Before that perhaps, LM Injection Reiniger or Bizol g80 or Mannol 9957 or STP Injector cleaner for full tank of gas or two. But best before the oil change so that it doesn't end up in sump with fresh oil.