there are a few adaption channels on the kv6 that can be accessed with the right equipment and reset, tps, iacv and a couple of others from memory, may be worth a shot first.

Problem is I need to find some one in Australia who can help which is pretty none existent

I use a vdo scanner that accesses this stuff as well as key programming, I assume the snap on and Bosch scanners do also? just standard garage equipment.

have you tried opening the tb butterfly a tad on the screw? that's usually all that's needed, the iacv is just out of range for the air needed with cams

You'll be lucky on Bosch the KTS was a nightmare on the MG/Rover cars would never get coms with any systems apart from maybe for few seconds then throw you out again. If you can find any one with auto diagnose that's what we use on them always works really well

Thanks guys will give this a go

Just to update on my issue. I decided to go over everything I had removed/disturbed in fitting the thermostat. Removed the TB, there was a lot of oil which had set like tar after the butterfly. I had cleaned some off when I removed it the first time but neglected the hard to reach parts like between the pivot points of the butterfly. So got to these areas with a cotton bud soaked in white spirits, made short work of it. All the edges of the butterfly that make contact with the inner wall of the TB. Both mating surfaces of the TB and inlet manifold, then reassembled tightening the torx head screws in a diagonal order (opposite corners) whilst holding the TB firmly in place the whole process with my free hand. I also checked the operation of the IACV and gave it one last clean with cotton buds and white spirits for good measure before reconnecting everything and firing up. Initially it was a still a little lumpy. That's no improvement at all I thought. Then gave it a blip on the throttle and the revs didn't drop below 700/800 rpm as they were doing before. That is an improvement I thought. It was also idling smooth again. But this was cold and the issue was always hot idle, so gave it a run this morning and it's definitely not doing the stalling and cutting out anymore when approaching a give way situation. The revs are actually holding around 2000prpm for maybe a quarter second when you come off the gas then dropping normally to idle (@770rpm). The throttle cable is set correctly with just the right amount of slack to allow the butterfly to close properly when the throttle is disengaged. But all in all I'm much happier with the way it is now running.

Also, try unplugging your IACV when it's idling then Rev the engine. When the revs drop the engine should stall. Plug the IACV back in and start the engine again. This improved my idling.