Fabia / Roomster take your pick starting issues

Hi all .  

I have posted a query on the Roomster mk1 forum but no replies, so hoping it may get a bit more attention and help here.  I have a 2007 Roomster 1.4pd 3 pot diesel with intermittent starting issues. It cranks for a long time before starting, then sometimes won't start at all then straight away it will start , turn it off and re try and won't start and so on !! I have replaced the glow plugs, The cam sensor, checked the feed to the cam sensor plug and all fine , i.e ground , 12 volt and 5 volt all ok . Could it be a fuel shut off selenoid sticking ? Or coolant temp sensor problem ? The battery is good showing 13.8 volts and I have taken the in tank fuel pump out and cleaned the strainer and blown all the pipes out in case of blockages and chescked the motor, all fine . Any ideas as going nuts trying to find the issue , btw my mate came here and it showed up on his diagnostics reader as cam sensor, fitted a new one and it wouldn't start at all, so re fitted the old one and at least it starts eventually , why would a new one not start at all ? Delphi make btw  . Thanks in advance Jon