What the heck is wrong with my altima???

[ivorton23]

Hey all you nissan guys....I'm having some issues with my 97 altima. Recently it started sputtering, idling really erratic, dying out and blowing out black smoke. It's been to the mechanic alot lately and even they can't seem to find out what it is. It has had the plugs replaced, distributor cap and rotor replaced(twice), new sensors(crank and knock) and the checked the maf sensor and idle motor.When I get it back from the shop it runs good for 2 days and then it acts up again and it's frustrating!! Does anyone know what could be wrong with my car?