The first thing that should be done is to get the diagnostic codes from the car's computer, this can be done two ways, the best way is to connect a code reader to the computer, most of the larger autoparts chain stores will do this at no charge, try Autozone, Kragen, Advance Auto or AAMCO. If that's not an option then the codes can be read using the car's check engine light by doing the following:
Turn the key ON
Locate the diagnostic connector under the hood
Open the cover and locate terminals TE1 and E1
Put a jumper wire between the two terminals
The check engine light will start blinking giving a two digit trouble code, for example if the light blinks once and then twice it would be a code 12.
Let me know what is found and then I can help to diagnose this.