As I have already admitted, I have zero experience of fault finding on ECU controlled fuelling systems..
I wonder if you have an air leak allowing for a weak mixture at tick over that has little to ne effect at highr revs... Yeah clutching at straws. I have used a length of tube held to my ear and moved the other end around the inlet manifolding and vaccuum connections for dizzy and servo etc... I have read of others spraying easy start with the engine running to detect such leaks but that seems to have potential to create problems..?
Good luck.
