Hi guys in the last week my td42t has acquired a small problem. When on cold start it will miss fire for a few seconds blowing grey smoke that smells like raw diesel. It only started about a week ago. I know it's not glow plugs as I replaced them about 2 months ago and it fires up straight away after the cold start its fine however sometimes after a 8 hour day at work it will do it others it won't. I tried today to glow the plugs twice which worked it didn't do it but I can't see it being plugs as they were Bosch plugs I put in and it fires first kick on cold start everytime but just misses and coughs and splutters for about 5 secs any ideas