P0130 code, sensor voltage and activity curiosity.

Good day.

Our car (2001 1.6 Octavia Combi) has shown us the check engine light a couple of times recently and before we had it fixed I borrowed a friend's OBD2 tool and had a look at what's happening. I have a few questions about what I observed.

The only code indicated was P0130, which indicates something wrong with the pre-catalyser sensor. This sensor is apparently a wideband sensor so not as easy to read using a simple tool as the post-catalyser sensor.

While idling generally the sensor in question hangs around 1.4 volts, STFT hangs around 0 give or take 1 and LTFT hangs around 10. At about 2000 RPM the sensor wavers between 1.4 and 1.5 volts with STFT around 2 and LTFT dropping to about 6. Up to 6000 RPM the sensor returns about 1.4 volts, STFT is around 0 and LTFT is not much above 1.

What I notice here is that the LTFT is always enrichening but this becomes lesser with higher RPM or load, which makes me think of a vacuum leak or exhaust leak.

Momentary full throttle and release seems to produce normal results, enrichening slightly then going lean then returning to the normal pattern for idle.

One further thing I notice is that periodically the sensor returns values of more than 3 volts, this often happens while the second sensor returns 0 volts. This seems very strange, it is infrequent and appears to have no pattern, or a least pattern too subtle for me to notice.

So, my questions are:

What, is the stoichiometric voltage for this sensor?

Does my analysis of the potential problem sound reasonable?

If not what would seem to be the fault and are there any other simple tests I could have performed to help identify the cause of the problem?

What is causing the strange behaviour with the sudden voltage increase on the sensor and why does it sometimes occur with the 0 voltage of the post-catalyser sensor?