It worked Steve, at least for now. I had to center the plate three times though, because it kept getting off center after short rides. A wearing on the pivot could be the phantom that moves the plate (hope not).
Fortunately, it has remained perfectly centered for a week now, after I used a locking compound on the central screw thread. The idle becomes smoother, almost silky, but for this little pulse every five or ten seconds, mostly notorious when the engine is reaching normal operating T°.
You describe a much more rough idle in case of a worn potentiometer, and given my lack of experience, I donīt think is worth (yet) to dismount the pot. My obsession with the idle goes now towards learn how to measure and regulate the KE duty cycle (thanks Bpaz). I recently replaced the O2 sensor, and according to what I've read in this great forum, it's good to do it.
Thank you, I really appreciate your advice and thoughtful responses.