Is the check engine light on? If so, do you have an OBD2 reader and can check the codes that it's throwing? How long has it been since the plugs/wires have been changed? How many miles on it? There are about a million different things that could keep your car from idling smoothly from bad plugs to vacuum leaks to damaged pistons. When did it start and did you do anything just prior to it having this issue?