Very difficult to tell if you don`t have the right test equipment.
You can measure the return of one injectors and compare with the rest, but that will not tell you everyting.
Best you can do is take all 5 out and let them test at a Bosch diesel specialist. Prior to testing they will put them in a ultrasonic cleaner to clean the nozzles.
In the test bench they will test the internal leakage, delivered mg diesel, opening time, spray pattern, etc.
After this test, you will know if they are within specs.
When you take them out for testing, mark them with a permanent marker so you know from with cilinder they came. This is because of injector trim that is stored in the ECU.
When one or more are defective and you replace them with new, you have to put the new "trim" value in the ECU. This can be done with "Examinar" at the dealer, or you can do it yourself with FiatEcuScan. The "trim" value is put on top of the injector.
ALSO first try to put your Airconditioning off... maybe the cause for the rough idling !