I have a 2014 Terrain, 2.4L 4cyl. There has never been a check engine light. The car starts perfect idles up fine then after about 30 seconds it stumbles rpms drop and it stalls. After it stalls the vehicle can be restarted immediately and after it's up to running temperature it runs great. Has never stalled once the engine is warm. Any ideas on what could be the cause of this?