Ok, I just ordered a set of torx sockets. The one required to remove the knock sensor bolts is an E12. I was able to replace the knock sensors fairly easily without having to remove anything else, using a ratchet with an extension bar. Fitting the new one was slightly more tricky but I used string tied to the end of the sensor cable to help guide it into position. The plug end was simple to to, just lift front end up on ramps and the end plugs in just up from the LH wishbone. Now I have no fault codes and no lumpy acceleration