Mine does that too . Actually it does it less now after I changed the spark plugs, wires, and air filter. Now my engine is a lot quiter and less harsh. Mine felt like the engine was jumping around under the hood. I was told that the clutch pressure plate was warped, so I took it to this place to have it checked out and they couldn't duplicate it. I think also my motor mounts are bad. Cars are so scared to go to the doctor so they're on their best behavior when you have 'em checked out.