Stringing: I am about to throw away the printer...
I am gonna give this a conclusion:
(Too) many factors are involved in stringing. Apart from the common ones (retraction, temperature, bad filament) there are many others... and I found another two.
1) After changing thermistor I had run PID calibration many times but the results were really bad (see above). Then I followed an advice I read somewhere: run PID calibration keeping the fan on. This was the real breakthrough!
2) The stringing test I was using was too demanding: it had a variable column section, quickly becoming too small for the nozzle that couldn't be wiped enough when going from left to right. Smaller the column section area, more the stringing (as you can see in the previous pictures). Then I switched to a constant column section.
I did the following test using 0.8 mm retraction at 190° (the rest is all standard Prusa settings). The left one is without z-lift, the right one with 0.6 z-lift:
It is not like the old days but still a good result.
Thank you for your support.
P.S. Sorry for the bad photos... I didn't take advantage of black friday... Still an old phone 😭
To confirm you mean the print fan speed, if so what speed did you set this at during the PID?