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Re: Laguna 2.0 16v petrol sounds like a diesel
If it sounds like a diesel then I'd bet it needs a new depasher / dephaser solenoid, which means a change of timing belt too (as that has to come off to get at the dephaser unit) Im afraid - not cheap all in all mate.
The dephaser could also account for your other problem.
Seeing as you've just purchased the car (and assuming you bought it from a dealer) then take it back and demand they sort it out. All trade car sales come with at least 3 months warranty these days.
Currently in dave_mezza2006's garage:
2014 Vauxhall Astra Limited Edition 1.4 16v VVT Turbo