OK, been a while as I've been waiting for parts to come from the US.
Fitted a new pressure regulator.
Doesn't seem to have made much of a difference. Still loads of afterfire and won't tick over on its own. It revs out OK above 3,000 rpm, just bogs when it comes back down
Ran it for a couple of minutes and measured pipe temps
1 - 176
2 - 201
3 - 220
4 - 124
So 4 is definitely cool.
Only other thing its started doing now is the control box is flashing long, short, short - which is air temp sensor. It wasn't doing that before.
I've pulled the sensor and its testing OK. Wires aren't broken as I've tested with a multimeter.
I've ordered a replacement air temp sensor in case its that, but I'm not holding out much hope.
Might be tricking trying to adjust the TPS at this stage as its not ticking over very well and I'll probably end up making it worse.
I guess only other thing is completely pull all the injectors again and check they're not blocked or sticking.