Hi all,
Thanks alot for all the help and good advice. It's really appreciated.
I toke up the "smoke test" advice first, since I realized I didn't do that. I had done a "visual" inspection of the vacuum hoses, and did the stupid assumption that was well enough. But the smoke test revealed the one hose I hadn't seen. The one below the intake manifold, coming from the ISV and going to the intake manifold. I couldn't see it at all from above.
Well the smoke test revealed it for sure!! :-D . I think the culprit are found or at least my fingers are crossed!.
I'll attach a few images:
https://ibb.co/LQ2XM3T
https://ibb.co/M5X4Jx4
https://ibb.co/kGZ4kSY
https://ibb.co/bsM4gLm
Now I've order the hoses and a few other spare parts. Eagerly awaiting their arrival to test if it fixes the problem. :-)
I'll return with the result next week when the parts have arrived.
Once again thanks for all your valuable help.