After I gave the ok for the replacement of the ecu, they called me saying that some wires were also cut and they too need to be replaced raising the cost to atleast 600e, but with no assurance if the problem would be solved.
As you can understand I informed them that I would take back the car.
I found the fsm on the web, checked for the error code and followed the steps, as they are described.
1. Chech engine ground,
2. Check Throttle control motor relay
After I replaced the relay the car was fine.
Obviously the throttle unit was fine, the ecu was fine, the wiring was fine,
but the specific official nissan resailer was surely brain damaged.
So the whole picture remains, trust no one, but only your logic.
Official resailers are certainly not what we think they are (atleast not all of them).