In the end it was a vacuum leak.
Obvious to my mechanic when I turned the engine off and the distinct hissing would bleed away.
It was a torn diaphragm in that round housing above the inlet manifold housing.
(Apologies for wrong terminology).
My mechanic simply squeezed with his fingers, the smaller rubber hose that connects to it, and the idle settled at 800 immediately while the engine was hunting the idle or settling the idle at 1000-1200 rpm.
(That's where I felt dumb after hours of my internet researching :-)).
Anyway, 2 minute job, $200 part :-)
BTW, service schedule book that comes with the car, mentions nothing about chain replacing, I mean, like never!?!?
But I should replace it eh? Can you hear warning signs?