1.5dci starts but misfiring

Hi all 1st post please be gentle! 1.5dci in a Nissan nv200 2015 I've had from new and regularly serviced engine starts 1st time everytime but for 1st 20seconds or so it's very grumbly misfiring and sometimes cuts out after 20 secs perfect no codes appear I've changed glowplugs and tested all good replaced glow plug relay, and today fuel filter still no joy fuel pump good running out of ideas....thanx