If the cam timing was out your would know, the engine would run rough all the time. I can’t really see how the spark timing could be out, but I’ll be the first to admit that I don’t know Rover engines inside and out, sometimes a faulty crank sensor can cause ignition problems, but most of the time this results in there being no spark at all so I’m not sure it’d be the problem. I also seem to recall that early K series engines don’t have knock sensors,
With regards to detonation / pre-ignition, have you changed the spark plug recently? Sometimes people replace spark plugs with ‘high performance’ spark plugs which are too hot for the engine causing it to pre-ignite, which can lead to detonation. If the engine was detonating then you would hear the characteristic pinking sound when it was happening. Pre-ignition may not cause as much noise but will reduce power, it also only normally happens when the engine is warm.
I would think however that the problem is with one the ECU sensors, the first thing I would do is make sure that the replacement coolant sensor is the right part, and if it’s second hand make sure it works. Next thing I would do is make sure you have the radio codes etc then remove the negative battery lead and leave the car for 30 minutes with it unattached, this should reset the ECU, which has a nice habit of getting rid of engine gremlins, reattach the lead and take the car for a drive to see if the problem still occurs.
If you still find that there is a problem the next sensor I would look at would be the MAP, you can clean it by soaking it in petrol, but for the sake of a £20 part which is normally pretty easy to replace I’d just replace it, then reset the ECU and see what happens.