So I had an auto electrician check the wiring and he gave it all a clean bill of health. EMS was reconnected, retuned and has been running great for the last 6 months, with no sensor value creep.

AEM repaired under warranty, even though the unit was out of warranty by 6 months, I only had to pay shipping there and back so props to them for that.

From all of this I learned to be more proactive and I should have been datalogging from the start which would have saved me heaps of time and money as I would have found the issue much earlier.