My two cents many things can cause rough idle. It is just what your willing to deal with and how much time and expense to correct. That said first bring all your services up to date plugs, wires, pcv, air filter if they are not already there. While you have the plugs out do yourself a favor do a compression test wet and dry it takes about 30 min. Take a look at the plugs they can tell you alot.
You can rent a compression tester from the some auto part stores. Make sure you have the throttle plates open when doing the test (I gently place a large screw driver handle under the throttle plates while doing the test) After all the services are update you can look for things like vacuum leaks maybe the plug reading will show a injector problem if that's what the problem maybe.
Other causes dirty MAF sensor, Idle control valve or a front O 2 sensor. For me I had a rough idle because my alternator brushes were worn out at warm idle the engine would move up and down 25 to 50 rpm after the brushes being replaced it's rock steady now so it was a voltage issue.
Don't get me wrong if your services are up to date then great. We see so many times that the previous owner put in the wrong type spark plugs or bad pcv . If you get everything up to date as they should be then you can look for something that might be wrong. While doing the service some times you find a vac leak or a bad wire. These are well designed vehicles and really very simple compared to to 80's and current made vehicles but many times they lack there services being up to date