Hello everybody and sorry for my silence as I wanted to report back when I resolve the problem. Unfortunately, I found the problem the hard way, unlike the dealer that just didnt know s**t. My DISA flew apart during highway driving and was probably the source of all this. Hope that none of its parts flew into the engine since it took me a while to notice by the fluctuationg idle again. I immediately pulled the still drivable car to the station, shut it off and after a succesfull start up which resulted in the idle jumping again inspected the engine - thus I noticed the DISA. I shut off imidiatelly and called a tow to the dealer. Let this be a warning to everyone who ignores the DISA maitenance. The cash I spent taking it to the dealer could have bought me a new one.
