My Plus8 with Gems has always shown as marginal on Lambda readings, usually near top end. In 2018 it needed getting plenty of heat into the engine to pass. Previously a mate used to take my car to where he worked as MOT tester and he advised trying cat cleaner. I did, on a low tank to increase concentration. No before/after results though so the effectiveness was not measured.
Last year the car went through ok with no issues. I have since put heat shield round the cats so hopefully that may help in future. Maybe exhaust wrap at some stage too to help getting the cats up to temperature.
