discovery td5 difficult to start when cold

hi, ive got a problem with my 1999 discovery td5. about a month ago it started to cut out when i first started driving it on a morning. found oil on the red ecu plug so put a new injector harness on it and cleaned the ecu out. it ran fine for a few days after this then it became hard to start first thing on a morning, decided rather than buy a full new engine harness, i would just chop out the oil infected wire and solder in some fresh wire. thought that would sort out the problem, it did for a few days. now i have changed the copper injector washers and o rings which someone suggested to me, this did nothing at all. now im thinking towards the cold start mechanism as it starts up fine once the sun has come out. i have noticed that the cooling fan seems to think the engine is hot as it is on all the time, changed the coolant temp switch today thinking it must be faulty. has anyone come across these starting problems before? im gettin desperate now im off on holidays in a couple of weeks and im scared it wont start when i need it to get me to the airport

thanks adam