I printed off the above threads to help prove that other Zed owners have had similar problems with their cars which in some case have been difficult to solve.
I took the car into the local Nissan garage today and spoke directly to the mechanic chappy who was very helpful and scanned over the printed threads I handed him.
He popped the car into the workshop and hooked it up to the computer. It still came up with no faults found but he reset everything he could which was linked to the possible fault.
It is waiting now for a replacement ECU which should have been changed as part of a recall for my car. He reckons that it may run properly once this has been changed so I guess I will just have to wait until then. At least then it will knock another item off the possible fault list.
Despite the reset today, she is stil running rough and jerky in 1st and 2nd gear.
I will mention the air leak possibility the next time I take it in next week.
Thanks to everyone for the suggestions, I will keep you posted on any progress.