My brother is a scrap man and is good at swapping things and crushing things lol but useless at any diagnostics

He bought a nice 51 plate 2.2 Astra with a knackered engine. So bought an engine second hand from a 53 plate Vectra (days later someone sold him a crashed 2.2 typical so now has a spare engine)

Anyway the vectra engine was tried in the Vectra and it went like a rocket.Now in has Astra it is sick, it runs rubbish to 3k then well to 5k and puts the eml on. He has done the pedal test and it reports nothing. So what to do to help him. I assume the fault is what killed the old engine too. Any suggestions would be welcomed. I don't know much about the 2.2 either