I'm so sorry you are experiencing this same problem. Neither my mechanic, Firestone, or 2 dealerships were able to determine what was causing the 'chugging / bucking' of my 1995 Cavalier. They replaced the fuel pump (which was only 2 years old) and everything else I described above and still no luck - the car was practically re-built and it still chugged and bucked randomly. I truly believe this is a defect of some sort with the Cavaliers and should be a recall. Personally, I no longer felt safe in the vehicle and since no one could determine what was wrong with it, I am now the proud owner of a 2006 Scion tC! Be careful and good luck. Cathie