Possible Booster Plug Problem
While trying to solve my fast idle I was advised by my van mechanic that it sounded like a problem with the air intake temperature sensor. As soon as I got home I disconnected the Booster Plug and put it back to standard.
The result was that I now have a tick over of 1150 but the engine warning light is now on. I took it for a spin to warm the engine and there was no lack of power so it's not in 'limp home' mode.
After a 10 mile spin I pulled up to see what the revs were doing at idle and they are fluctuating between 1050 and 1200 - Still not correct but a big improvement on what was happening with the BP fitted.
This doesn't necessarily mean its the BP that's at fault but tomorrow I plan to do the 12 minute tune again without the plug to see if the revs go down further.
I've just ordered the Dealer Tool to see which error code it's now throwing out, strange it wasn't doing it with the BP.