I swapped 6th injector with 1st last night - no difference - 6 cyl is still not running properly. I expect it is something to do with the valve. It will be expensive i expect but i may look at doing some further work to the head while it is off.

Just had compression test done and compression is really good in all cylinders. Now i am really confused and the mechanic is a bit stumped. We both thought it was a burnt out valve. Idle is the only problem when reving above 2k it is fine.
I am waiting to change my cat converter because it is rattling. I think that it may be partially blocked and causing the idle problem. Does this sound possible?

you said that u changed the injector, was the just the injector? if so try changing the actual lead for the injector (say change the 6th to the 5th injector) see if this makes a difference. It might be just a simple case of a broken wire

Good idea i will change injector lead tonight - let you know how i go.

Well at least that is some good news!