Here is a walkthrough of possible causes. It is a process of elimination. So, eliminating all that you can will be a great help and make the outcome much more likely that it can be solved faster.
The first thing you should do is have the trouble codes pulled at an Advance Auto ro Auto Zone, they do it for free. Even if you don't have a malfunction light on the dash does not mean a code can't be pulled that will elimate a lot of possible causes.