thanks GIsnickers, I think I could apply probably those two if I have to choose because the others look good.

Check the frequency and amplitude of the oxygen sensor (advanced)
Check for a deteriorating / contaminated oxygen sensor, replace if necessary

 

BTW, how can I check the frequency and amplitude of the oxygen sensor. I have an access to the osciloscope, but what kind of measurements should I be expecting to get ???

 

This past weekend I tried running the car only on a spark antifouler plugs. I disconnected the O2 simulator completely, and lets antifoulers in. Guess what, still does not work. At this very moment I tried everything I could, and run out of suggestions.

 

If you have a good OBD-II scanner you can watch both O2 sensors at idle. You should see the first sensor oscillate between about 0.1 to 0.9 volts. The second one will also oscillate but in a narrower range about 0.45. If sensor 2 tracks sensor 1 too closely the ECU decides the cat isn't working and sets the (0420?) code. The mechanical fix damps some of the oscillation and usually works well.

Dave