This could be a lot of things. I think it's probably best to give more information and collect more information. This is the N20 engine, right? How many km are on the vehicle? I would scan for codes. The n20 engine is the one with the timing chain issues, has this been resolved? As far as I know that repair is something that should be done no matter what. When not if.
Any noises the car makes? What's it like on a cold start? Any rough idle? Any drop in RPMs? Check under the hood for classic oil leaks.