My 2000 Nissan Xterra is giving me fits. I have had it to 5 mechanics. It is still not running right. (I'm a female) It was dying on me. The rpm would go up and then down. It would not idel. I have replaced: knock sensor, mass air flo sensor, dist. Cap and rotor, replaced plugs and fuel filter. It is running better, not dying but there is still a problem. Any suggestion on what to replace now?