brother the gdi engines are no good they are common failures , the idling at N is normal for these big engine cars but the fuel cutting of is to do with the GDI system in the engine, they are rubbish engines, i have had them in the past they only good for parking up and rotting away lol, they are plenty od these here in the UK only some you will find that are working perfect that would be if they had £££ spent aswell