[BimmerBum]

I edited the post to say sensor instead of sensors.

You are correct, there is only one O2 sensor on the M42. It is before the cat. If the cat is clogged then removing the sensor will allow some exhaust to escape (rather than trying to find its way though the clogged cat), idle, etc should improve but it won't be perfect with the new hole in the exhaust and O2 sensor not doing its job. You are looking for improvement over the current symptoms. This is not a solution and this is not a way to drive the car, this is just for diagnostic purposes.

You can come at the knock sensors by removing the intake manifold (upper and lower) but you can also get to them by removing the oil filter housing etc. Personally, I would rather go the oil filter housing route. That is how I did them on my Club Sport.

Like mass air meter codes, knock sensor codes are often just a symptom and not the actual problem.