I have a 2004 cavalier with the 2.2 ecotec engine as well. Had a similar problem. Mine would not stall, but it would be jerky in third and fourth gear when driving slow. And at least 4 times it reved up while driving as well to around 3000 rpm. Push the clutch in or slip it into neutral and it would stay reved until I hit the gas pedal. Once it reved back and fourth between 2000 and 3000 rpm all on its own while the transmission was in neutral. I took it back to the dealer and they found a new update for the idle. Downloaded it from the GM site in a few minutes and then uploaded it into the cars computer and I have not had a problem with it since. That was about 2 weeks ago now. HOpe this helps. It was a quick easy fix. And free of course.