Engine oscillations / power loss

Love V8 friends

I am new here and I am not sure whether this communication will also appear in the forum.

Coming from Switzerland, driving a V8 3.6 for almost 4 years, built in 1989, and browsing around with enthusiasm in this forum. Unfortunately, I am now also affected by a more serious technical problem, which is why I am now looking for help to you. The following problem: Cars brought to the annual inspection plus additional work every 30'000 km in garage of my trust. I could not mention any defects in the garage except the idle problem when starting on a warm machine and lighting up the warning lamp for hydraulic/brake fluid in fast curves and strong brakes. Inspection carried out, Idle controller cleaned (thanks to the forum) and brake fluid refilled. Cars full of joy picked up and comfortably drove home. The next day, easy plucking when starting, restless idle, but stable when starting (return of the controller has brought something). Over the following days more and more dropouts, only at higher speeds nothing, engine power still squeaky as before. Put back in the garage. There you have changed both OT-Geber (defect memory read out), then also reverberator and 1 hit ignition cable. Picked up the car and what now? When starting, especially after cold start, shakes in the partial load range and is a completely lame duck even in warm conditions. Nothing more with a strong thrust, just a comfortable turn up. What can that be? The Lambda probe is fine, by the way. The fact is that the car had neither a dropout nor weak on the chest before the inspection. Can anyone help me here? Could the engine cleaning have penetrated moisture somewhere? Maybe it's just a little something. Anyway, my workshop seems to be baffled.

I thank you for every hint I can get and wish all V8 drivers a lot of joy with the really great car!

Patrick