What could it be? Car was sputtering and hard time taking off at first but then it's fine. So we changed spark plugs. Test drove was good but at start up there was idling. On highway stranded bc the car stopped accelerating making a loud clicking noise and eventually engine turned off on its own. Pulled into nearby store only barely making it. Temp got hot, light smoke and burnt smell from hood. Air blowing out near engine and oil. Put water, a whole lot of water after letting it cool down. Started it up ok. Then turned off again.