hi , some times my rrs drives like a dream and then some times the power steering gets a bit stiff , 05 tdv6

Have you ever changed the fluid ? Easiest way is turkey baster. Make sure fluid is at correct level in reservoir (if ti is low that could be your problem). If fluid is dark - needs changing. Siphon out as much as possible. Refill reservoir to correct level with dealer fluid (or GM/AC Delco Cold Climate fluid - not sure if that is available in UK). Run car for a day - then do the same again. Once you have use the whole quart bottle - you should have mostly new fluid in the car. (Or go to indie and have them do a full flush if you want to spend more). Also check accessory drive belt is in good condition (no cracks, cuts, ribs still look good - not too smooth) - if that is slipping , it could also cause you problems.

Check the suspension ECU for fault code C1130.

If this is present, it is an issue with the sensor on the steering rack

If it is not, then usually the lower column is at fault

would that make the problem come and go

The column would, and if the wiring was an intermittent issue, then yes again

bottom uj on steering column , drives spot on now

Mine is the same, but black fluid in the bottle. I had the indie swap it and it drove perfect a week. But back black agian