2006 Ford Taurus

Well my rpms are still flucuating. I cleaned the battery terminals, tested the the battery and the alternator both tested good. I changed the spark plugs, and the fuel filter. Replaced an intake boot cause it had a crack. Check the vacuum lines they look good. I cleaned the idle valve, and cleaned the throttle. All my air filters are clean and the fluids are all ok. The other day the check engine light came on and the scan tool said random misfire. Its done that once or twice but the check engine light has gone off and has stayed off right now. Also when its sitting at a idle when the rpms flucuate it feels like it is going to die, but it doesnt. I still wonder what it could be? I, ve replaced the sparkplugs again and still did not help.