OK Thanks Trevor,
Just to be clear........ you're saying from what I've told you, you think I should replace my existing sensor (and then I will need to set up correctly) or should I carry on adjusting the existing sensor because you think it's only the position that is wrong and I should continue adjusting slightly each time until it comes right?
The Nissan agent did say they sold a lot of replacement throttle pedal units.
Like you say I'm also suspicious about the wiring connector because the last time I was adjusting the position of the sensor, I would have been pressing on/moving the wires/connector as there's very little room to work. It went into limp home mode but know I didn't disconnect the connector. So there might be a joint or baynet contact in the block which isn't making a consistent good contact. So when/if I get it sorted I'll zip tie them in position.
Thanks again, I'll let you know how it ends. Simon