Just to follow up.
Got car in workshop. It was the AVCS filters. The filters on both sides had come apart (below the Banjo bolt). Meaning the solenoid couldn't push the valve up and down correctly. Both valves were stuck in one place because there was tiny bits of plastic stuck between the housing and outside of the valve. I took the solenoid out cleaned it thoroughly. More broken bits of filter came out. Tested the solenoid. Put it all back together and boom. Car working!!!
So now I need to put in new filters and washers and an oil change and good for another 10000km. Thanks for all the help guys.
Still have engine light but I'm leaving the battery off for a while hopefully the ECU will forget!
It always pays to check the simple stuff...
I had the gauge plugged into metre output 1 on the gauge controller and turns out it needed to be in metre output 2.
All working as it should now.
Thanks! I've gotten in touch with Corgiwerx and have a set of both linkage and pivot bushings on the way. Can't recommend the guy enough so far, fast and easy to deal with and for a very reasonable price. Will update once they're installed.