Hi and welcome to the forum [emoji4]
There are a handful of reasons... Most easy enough to fix. Does the engine light come on?
Was it left standing for a while before you acquired it?
Keep driving. Once the engine is hot linger in 5th or 4th when it might coast in the higher gear, give the engine work to do without free running it. It might go away or you might trip the engine light.
If it was a dealer buy let them know, depending on your deal they might have both a responsibility and ideas. Either way get
Multiecuscan and the leads, check the fault code and report back as guess you will want to be self sufficient over time [emoji106]