Have you checked your cars computer for codes with a scanner of some sort? You can use your own, borrow a friends or co-workers, or go to a parts store like AutoZone and have them scan it for free. If no codes, check your fluid levels for everything, have your battery and alternator tested, look for vacuum leaks, disconnected hoses, wires or sensors. Finally, consider any recent repairs you may have had (like throttle pedal or sensors). Please let us know what you find or remember.