Yeah but because I've blocked the egr valve I wanted to find out if it was something simple before I uninstall the blanking plate to take it to Nissan. The Blocked EGR valve made too much difference in power and economy to write it off and remove the plate without trying everything else first.

Logic says it would be to do with the egr but it's been blocked for weeks with no dramas and by the comments on the forums it seems that the engine goes into limp mode if there have been any problems, albeit rare, with the egr blocking. I don't want to uninstall it and find out it was a dodgy sensor somewhere completely unrelated or something like that.

Removing the plate will be the next step and it will need to be soon though.