Jackie lets start again - this thing is running away with you. The timing chain is notorious for giving problems on these as it throws sensors out of alignment.
However, your light is on. So, get a garage to clear the fault codes with a scanner, and then do a dynamic test on the car - ie driving it along with a scanner connected. The new fault codes can be read, and maybe you'll get somewhere. Maybe a Nissan main dealer could be the best bet here...and thats unusual for me to say that!
John
July 2009