starting problems

Hi - joined the forum in the hope of some advice. My 03 pathfinder [ approx 58000k] starting being difficult about starting in the summer. it would rev/slow until warmed at first [ and stall if it didnt warm up first] then progressed to requiring the engine warmer on to start [ in summer] So i took it off to our local dealer who £150 later pronounced it prefectly healthy with no reason it wouldn't start. They just were not interested in my protestations it wasn't right. So we limped on with at least 5 attempts being the usual before spluttering into life and frequent stalls until warmed up]. The local garage has no ideas either.

Now at morning temps of below zero it just isn't doing. The wife refuses to take it to work in the snow because of fear of getting stuck at work. Any ideas - or good nissan mechanics in mid essex ?