A UK workshop replaced an engine control unit as part of an unrelated electrical repair.
After the vehicle returned to operation, the engine started normally but developed a rougher idle than before.
Because the injectors had not been mechanically changed, the workshop initially expected their previous behavior to remain unchanged.
Diagnostic review showed that the control configuration needed further attention.
Some diesel systems use individual injector calibration information.
This data allows the control unit to account for small production differences between injectors.
After control-unit replacement, programming, or certain software procedures, injector-related information may need to be checked again.
If the control unit does not have the expected data, combustion balance may change even though the physical injectors remain the same.
The workshop still confirmed:
No mechanical injector fault was found.
Attention then moved to the ECU configuration and stored injector information.
ECU configuration problems should be distinguished from faults in the injector electrical circuit. For a related example of a different troubleshooting path, see this injector wiring fault diagnosis case.
The required injector data was reviewed and entered according to the engine's control procedure.
The engine was restarted and allowed to stabilize.
Idle quality improved without removing the injector set.
Modern independent workshops in the UK increasingly perform electronic control-unit replacement and software-related repairs.
This creates a new diagnostic boundary: a vehicle can develop injector-like symptoms even when no injector has physically failed.
This UK case demonstrates why injector calibration should be reviewed after relevant ECU replacement or programming work.
A rough idle appearing after electronic repair does not automatically mean that an injector failed at the same time.
Mechanical and control-side verification should be completed together.
