Just a note on the knock sensor: I recall reading (here) that it is very
particular about being tourqed correctly (I suppose it is a sensor under
stress). So, if it is replaced, make sure the person doing it knows
what they are doing and has a tourqe wrench thats callibarted for low
torque settings (14.76 lbs for the sensor(s) on my 98).

The info at alldatadiy.com describes how the sensor works but not what
happens if it fails (that is, it did not say if the timing is retarted).
It also describes the steps to replace. Cost is $25 a year to subscribe
to alldata (I don't work for them but find the data useful).