My girlfriend's Nissan was idling rough and low at around 400 rpms, and would stall the car if I turned the A/C on. I removed the throttle body boot and cleaned the throttle bottle, plate, and inside the TB with Throttle body cleaner. Itís critical that you use an approved Throttle body cleaner and not just a carburetor cleaner. The throttle body has parts that are Teflon coated and pure carb cleaner will eat this coating off. I used Valvoline SynPower Throttle Body and Carburetor Cleaner for $2. I wouldn't think that after 12,000 miles you would need to do this, but usually rough idling is a result of a dirty throttle body, fuel filter, air filter, or faulty injector. If all these check out o.k., check your distributor cap and rotor. You can check your injector(s) by using a long screwdriver and putting the tip against the injector. Put your ear against the handle while touching the injector with other end of the screwdriver and you should hear swishing and clicking if the injector is working. Or you could get a stethoscope. With only 12,000 miles on your car this is kind of mysterious. Most cars have a idle screw that can be adjusted but this would be my last resort. I'm not a mechanic but this is what I would do to troubleshoot if it were my car.