After swapping over many different parts (Thanks IAN332i) I gave in and took it to a local guy who has a very good reputation on performance & race engines.
He stuck it on the diagnosics and it showed up oxygen sensor. So got a new one and took it back to him yesterday. He fitted the new one but no improvement.
A quick look at realoem revealed the OBVIOUS problem.
When the exhaust manifolds were being modded they mixed up the Oxygen sensors. So the readings from O2 sensor 1 was feeding the ECU data which it was then supplying to bank 2 (cylinders 4,5 & 6) and vice versa.
I am one happy bunny!








