Unfortunately it could be a number of things causing rough idle It sounds like the engine might be confused about how much gas and air it is getting which might mean it needs a new oxygen sensor (EMISSION) or throttle position sensor. Start with the easy maintenance items like spark plug wires, air filter, and fuel filter if they have not been replaced recently. A bad spark plug wire may only occasionally short out and cause these problems. Try looking under the hood in the dark with the engine running and see if you see any electrical arcing around the spark plug wires or just go ahead and replace them if they are old. It might just be a clogged fuel line/injector/ or pump, try to put some fuel cleaner in tank the next time you fill it up and see if that helps. but I would also have to check out a couple more things such as the MAP sensor,and the o2 sensor. Check for vacuum leaks, also be sure to make sure the iac motor is not stuck out or has a loose spot. Get a Vacuum gauge and monitor the engine vacuum ...Also make sure that your O2 sensors,map sensor, coolant temp sensors are all functioning normallay.... try a fuel system clean (not the junk you buy at the auto parts store...have a shop perform a system clean.
