57 vectra 1.9 cdti starting problem?

hi i have had a 57 vectra 1.9 cdti for nearly 3 years now and its been a pig to start all that time.from cold usualy starts in around 4 seconds,if i nip down the road and engine not fully hot ,no way will it start,has to cool right down, when its hot it starts in about 6 seconds spluttering most times before it fires, iv also had the spanner light on dash as long as iv had it ,vauxhall came up with cam sensor but no difference, iv changed starter motor ,it is a taxi and struggled all the time with it, help