I’ve been having a similar problem recently with the addition of a misfire an ensuing belch from the exhaust. It is also a K Series 1800 with Emerald K3 ECU on Caterham TBs and I suspect it is heat related, however, those that I have consulted are not convinced. Both TPS and coil pack have been suggested as a possible cause, along with a dodgy temperature sensor to ECU. TPS adjusted and TBs balanced by Andy at PGM, plus I have changed the sensor along with plugs & leads and it appears to behaving itself.....why did I say that....!