Lee : The idling issue could be an issue and perhaps ties in with some vacuum leak and or air leak upstream of the MAFS (unmetered air)
I get them from
Just Lambda, Suppliers of zirconia and titania lambda sensors by post I think. The ones you want are Bosch 13477 but double check with me, if you like, before ordering.
Wayne : Yes mate, keep it running on 99 (the first thing I asked you when I got out of your car is "Oi what fuel are you running ???" ...You have such a nice example of the car, feed her what she wants !! Nice meeting you too man ! We'll chat properly the next time we all meet up.