It could be many things, unfortunately and without experiencing the problem first hand or being able to do some basic diagnostic tests its hard to say. It's best to start with the basics, is the engine mechanically sound, even compression, no vacuum leaks then verify fuel pressure and quality of ignition spark. There is a company that independent auto repair shops get their information from, this same information is available inexpensively for people that work on their own cars.. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online