Take off your idle air control valve and clean it. Use Seafoam, intake cleaner, carb cleaner, whatever. This would be a good time to do a Seafoam treatment as well. Also clean your Mass Air Flow Sensor and replace air filter, spark plugs, and fuel filter. You will find all of this will improve your gas mileage in conjunction with your rough idle.
Performed in this order makes the most sense:
First: Idle Air Control Valve and Mass Air Flow Sensor cleaning, and Air Filter Change
1. Take off battery cables.
2. Disconnect IACV and MAFS plugs.
3. Remove IACV.
4. Clean IACV with Seafoam (or equivalent) using q-tips and let thoroughly dry (compressed air is convenient here).
5. Remove MAFS.
6. Spray electrical NON-RESIDUE contact cleaner onto the two wires/probes. If your careful, you can clean it with a q-tip soaked in the electrical cleaner. Make it dually noted that if you bend or break those wires you will be buying a new MAFS.
7. Change air filter.
8. Reinstall MAFS and IACV and connect corresponding plugs.
9. Reconnect battery cables.
Second: Proper Seafoam Treatment Procedure (I found that nobody really knows how to do this right), Fuel Filter and Spark Plugs
1. Dump 1 full can into gas tank.
2. Dump 1/2 can into engine oil.
3. Take plastic air inlet tube off throttle body. Pour 1/2 body into a spay bottle. Start engine and idle around 2000RPM or so by pushing down on the spring and lever that controls the butterfly valve on the throttle body. Squirt all the contents of the spray bottle into the throttle body. Do not let the engine stall.
4. Turn off engine when done.
5. Wait fifteen minutes. During this time replace plastic air inlet tube on throttle body. Pull the battery cables off the battery for 10 minutes to reset codes thrown by the MAFS. After 10 minutes replace battery cables
6. Start engine after 15 minutes and go for a ride til there is no more smoke coming from tailpipe.
7. After 200 miles, perform an oil & oil filter change, fuel filter change, and spark plug change.
All of this will take about 1 1/2 hours and cost $40 at most. You'll make back that money in MPG by two fill-ups at the gas station.