Well, the easiest way to identify the fault would be by a diagnostic check, this should show a fault code, ie P ---- 4 numbers which can then be used to narrow down the problem.

If not a diagnostic, then you would need to check the following:

1. Air Filter restriction

2. Intake system air leaks

3. Condition of fuel filters /pipes

4. APP (accelerator pedal position) sensor

5. Injectors

6. MAF (mass air flow) sensor (if fitted)

7. Turbocharger (TC)boost pressure sensor (if fitted)

8. TC bypass valve (if fitted)

9. TC Waste-gate regulating valve (if fitted)

10. TC Wastegate

11. EGR (exhaust gas recirculation) throttle control valve (if fitted)

12. EGR valve position sensor (if fitted)

13. Fuel pressure sensor

14. ECT (engine coolant temp) sensor

15. Camshaft position sensor

16. CKP (crankshaft position sensor)

17. Exhaust/cat restriction

As you can see, there are many things it could be, hence the diagnostic check.