2001 Other Peugeot Models Emissions failure issue

Hi,

I have a Peugeot 106.
My car has failed its MOT due to emissions 3 times now. The following has been changed/repaired: CAT, both lambda sensors, ignition coil, its had a full service and there are no leaks from the exhaust.
Still the car fails on CO at high idle and at an engine temp of 90oC. The dealership haven't got a clue and have refunded all labour. Its is worth noting that the exhaust sounds bubbly from time to time. Any help would be greatly appreciated.....?

Thanks
Gary