I am at a lose the p0300 comes on all the time. I changed
distributer cap rotor and wires
fuel pump
all injectors
fuel filter
cats
mass air
map
plugs
thermostat
crank sensor
coil
I am at a lose need help
car has 66000 miles

 

What exactly are you driving?

 

Have you done a complete fuel pressure and leak down test series?
Have you connected a vacuum gauge to check for leaks and fluctuation?
Have you done a compression check?
Hopefully you did these test before buying all those parts.