if the fuel trims go negative it means its running rich, not as many things cause it to run rich as lean. my car had a similar problem and i flushed the injectors and it fixed it. also worked on a truck that idled rough and a flush only fixed it for a few days. pull the fuel rail and cycle the key from off to run a couple of times. don't crank it over and see if any fuel is spraying out of any of the injectors. none should come out