Fiat Seicento Sporting engine management help required please

Hi
New member here who could do with some technical help

2002 Fiat Seicento 1.1 MPI

I recently bought the above car as a none runner caused by immobiliser fault and to cut a long story short ended up buying and fitting a second hand ECU and all associated parts
On fitting all these the car starts and runs

The problem I have now is the EML constantly flashes and the engine runs rough especially at idle

I have scanned for fault codes using my Autel AL419 and there are no live or pending fault codes

I'am unable to run the car on the road due to no MOT or tax

Any help greatly appreciated

Regards
Mark