Help please. Same code differnt symptoms

Hi. I have just completed an engine swap on a vvc freestyle. This included new head gasket and cam belts ect. The problem, EML. P1521.



Now there is no sympton. It ticks over ok. It revs correctly to over 7k. It drives fine. If i clear the code it soon comes back.



Now ive tried un pluging and checking what code appears. The brown vvc plug brings up the same code as an addition. The same with the black. The blue one does no change apart from origginal code. They are pluged in that order.



The car has been standing for a few months where for some reason the previos owner had taken the fuel pump top off .



Have read previous posts on this code but cant find solution to this problem.



Cheers

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