2002 vectra dti starting problems?

had problems starting my 2.0 dti vectra,local vauxhall dealer told me it needed a new injector kit so went ahead and got this done at a cost of £200 but to no avail, when i returned it they had the car for 3 days but could not find any problems (the computer was showing no faults)and told me they had exhausted all avenues and the only thing left was the pumpat the extortionate price of £2500 but they could not guarentee it would cure the problem.i then got a bosch dealer to check the pump but he could not find fault either. after 6 weeks of heartbreak i spoke to a mechanic who then disconnected the engine coolant sensor and told me to try car for a week. the car started 1st time every time(with glow plug lights coming on) so got a new sensor, but now the starting problem has returned.help