Check to see what kind of color you have on the spark plugs. All 6. You may have a leaking injector. If you have a plug that is black, that maybe a bad injector. If all are black you have other problems. It could also be the Air flow meter or a stuck EGR valve. Get a manual (Haynes or factory) and fallow the trouble shooting section.
Not really easy to fix anything with a computer now days.