Dieter,

I have waited to respond because of all of the help you've been getting.
 After reading about the many O2 sensors, I feel it's time to look at
the FUEL PRESSURE Regulator.  If you can, verify that the Fuel pressure
is around 30 psi at idle and no more than 36 psi while driving up the hill.

If the fuel pressure regulator is worn or stuck, high fuel pressure will
cause a rich mixture, that the computer cannot compensate for.  Result
is a O2 sensor with soot covering it. But the real problem is not a
failed O2 sensor, it may be a worn fuel pressure regulator.

I have used a propane torch to burn off the soot, and the O2 sensor will
work again.

pmail, and I'll walk you through the procedure.

Sincerely,

Mark Keller
91 Carat
Cowichan Bay, BC