First off, guessing isn't going to get anywhere other than a lot of money spent on the parts cannon.
Get the car scanned for any codes. Even a Pending or History code is better than nothing. Once we get that info, we will go from there. In the mean time, what things have been done in the past 6 months/year maintenance wise?
Also, please do not use "please help" in the title. We already know you need help because you posted a question here.