Omega MV6 does not start properly and runs round when cold

First of all, hello to everyone here in the forum, am new here and have the first question right away. So the car: Opel Omega B MV6 BJ 1998 km 185000 automatic So now to the problems: So I had various things done at about 165000km like ZKD, valve shaft seals, tooth and rib belts, WAPU and a few small things. So far it was running top, but the problems start again. When it is cold and is started there is a strange loud whistle in the engine compartment, this is nac h about 1-2min away. The speed also plays a bit crazy. Sometimes with a little over 1000 then it goes short to 500 and then again 1000. this plays 3-4 times. The bigger problem however is that it gets warm very quickly. in cold weather so at 93° in warm weather and during long rides also in cold around 95° or a little higher. however, if I then park the car, especially after longer distances, the fan runs only shortly after about 10 sec. I then want the car 5 min later sta rten is the temp at about 97° or higher and it does not start. Must then wait half an hour or so. If I drive longer distances and it is at 95°, other things also occur like e.g. the servo becomes weaker, steering wheel is difficult to rotate or the automatic switches very jerky. hope I could explain it halfway. would be happy if you can help me. I know that a remote diagnosis is difficult;-). many thanks in advance MFG