I was at PGM earlier in the year for them to set my car up and, amongst other things, another rough-running 620 was a topic of conversation. My understanding is that the Caterham set-up/map is a flawed compromise and is never going to be optimum as its ECU map doesn't use a full/ideal set of inputs/parameters to determine the ideal fueling. PGM's solution as I see it (worth having a chat with Andy - he'll explain better and given his character and how busy they are, you won't get a hard sell!) is to take a step back and remap based on different/additional engine inputs. The result is the car the 620 should be - no over-cooling, no over-fueling (and so potential bore score) just a proper, smooth, bonkers-fast car. Whilst it wasn't their objective, their solution in some cases has also released getting on for another 20% of power! This may or may not be where your problems come from (how many faulty lambda sensors are there out there? ) but certainly worth investigating...