Even despite an inordinate amount of advice from members in
this thread we basically ran out of steam in terms of diagnosis, and yet, I couldn't escape a couple of niggles blighting me.
Why couldn't it calculate load properly?
Why was anything past 49% of throttle "invalid"
Why did speed pulses appear and dissapear?
Yet everything else in terms of data looked OK?
Seems the Y26SE has some funny foibles when the ECU is duff. I've never seen one so perfectly reproduce such a bizarre / specific fault.
Anyway, despite advice to the contrary I leapt (too ambitiously perhaps) at the first ECU that was available with 2 chips and the barrel. Member
Twiglet got it in the post and I had it the next day (thanks for the other offers too - testiment to the site that I got several replies!).
So I fitted it this morning in the pouring rain this morning, and whilst I have the orange spanner (I'm assuming because it still has the auto programme that I can get Tech2'd away) MY GOD IT WAS GOOD TO GET IT FLYING AGAIN!!

Almost as nippy as the 3.0, and as good if not better off the mark.
So I Just wanted to say thanks to everyone that replied!!

I'm now a member of the elite club of people where it was the ECU all along! Going to have to take it to billing instead of a MK2 now as it's so clean.