The Guys have also been investigating the fuelling issue at idle.
My initial thought was that it was overfuelling, but the have tested the AFR and it is actually substantially underfuelled

So we are planning to fit a piggyback ECU and doing a complete adjustment of the fuelling on their dyno.
I wouldn't get a piggyback ECU fitted. There will be a reason for the issue, otherwise you are just masking over the problem by going piggyback, plus piggyback ECU's are so 90's

It might be worth speaking to FC Performance to see if they can advise as I believe they mapped the car
My Mapper has already spoken to FC about the car.
It would appear that the issue is probably the lack of mapping points on the original ECU. Because the rev limit was raised it has used up more of the mapping points and has not left enough to fully map the idle and cold start. Also the oversized AFM doesnt help!
Piggyback ECUs have improved hugely in recent years and are now probably more powerful than some of the top end standalone ECUs used in years past

Hopefully he will have everything done this week and I will report on the results.