would also like to know the answer to this as my old 3 dr used to do this ???

i tried allsorts inc map sensor ,injectors ,chip+ecu, gaskets, sensors,

basically allsorts and still did it
although mine always ran sound after a few second on three cylinders and also made good power 371bhp
just always use to piss me off when my mates laughed at my three cylinder cossy lol on startup