noisy engine. difficulty starting. loosing power

Purchased 8 month old car from VW dealership in Towcester UK. Told car probably belonged to little old lady as had low mileage. Later found out was ex rental from Europcar. Engine very noisy from beginning advised to keep windows closed and turn radio up. Car drove okayish, had episodes of loss of power then power surges. Very jerky drive. After owning car for 4 weeks car would take 10 -15 minutes to start and keep running, engine would be nearly shaking out of bonnet .VW rescue could find no faults on computer nor could they get it running smoothly. Car returned to dealer. Told it is a software problem. No recall notice found anywhere though !!. Will go and test drive car tomorrow not sure if i want to keep it as i have been misinformed to previous ownership. Might test drive a 1.4 instead. Funny how they are all over you in the showroom then once you've handed over the money they don't want to know. Car purchased for 18 year old son who just passed test. Wanted to know that he was in the safest reliable car possible. Not so sure now.