Hi,
The lambda probe should typically have a lower voltage less than 200mV and an upper voltage greater than 600mV, as the GS911 shows us.
If the upper voltage is less than 600mV or lower voltage is bigger than 200mV, it has a problem and must be replaced.
What should be the response time (in the time domain) of the lambda probe in milliseconds? This can be measured easily with the oscilloscope.
This is important because if the response time is longer, there is problem to the ignition adjustment.