Metal grinding noise with knock

I have a 95 nissan maxima that we just dropped about 600 in repairs over
the last 6 months. We just replaced the fuel and air filters, and the pcv along
with it's grommet which incidentally the old one fell into the valve cover after
being torn to shreds by pliers. I have also been losing torque gradually for
the past few weeks as well. The car ran could for about 14 miles and then
the metal grinding sound began I turned the car into my neighborhood and it
stalled pretty violently. It was stalling before when the idle was at 4 to 500
rpm which when tested the alternator wasn't putting out hardly any power
causing dead cells in batteries. We raised the idle and it ran perfectly battery
was getting power and my ac was working even (having not worked the
whole time I've owned the car). After raising the rpm and all that everything
started working and we added in some heat and something else to burn
sludge and all that out of the motor. Like I said this seemed like it was a
temporary fix because it stalled and wouldn't start after that. So in other
words could their be anything else besides the grommet causing this or
could it be the grommet? I also replaced the serpentine belt after having the
care for a month which to this day I'm still not sure I got it tight enough.