it could be something quite simple like a spark plug or lead broken down,just take it to your local garage,tell them its not running right and they should find the fault just by listening or having a little rumage round the leads etc.
just a word of caution. took my diesel in for diagnostics, they told me that the computer in the car had recorded so many faults that they didn't know what to look at, so they left it. still charged mre �60. though.
Before you go shelling out for diagnostic tests, firstly check the electrical connections to the injectors: these have to carry signals to tell the injector to open and shut anything up to 7 or 8 times in a microsecond of injection time, and the connections need to be clean and secure.