Air filter?

Steve.

Get a real car?

Sounds like a fuel problem, to much fuel can thin the oil and wash the
cylinders causeing a black smoke problem

see how quick the plugs are fouling, pull some plugs see if they are
washed and wet with gas, another way pull some plugs and run the motor
with a white cloth over the hole you should have quit abit of gas mixed
with oil.

Check the level in the pan and see if it is high as well gas will run
down to the pan if the following is happening.

I had a simular problem with a CPI the regulator went bad on a non
rebuildible BOSH CPI unit 550 dollars later it was fixed with one part
the CPI corrected problem at once. It could have been more had I let the
dealership put it in 550 was for the part alone, only thing that I
replaced after that was the O2 sensor that was damage from all the live
fuel that washed accross the O2 sensor and in to CAT damaging the unit.
That was only 36 dollars and had it not been causing a check enginge
light and seom fuel milage I would have left it. If you do replace the
O2 sensor Put some High temp Never seize on it.

Here is another tip before attempting to remove the O2 Sensor get the
engine nice and hot O2 sensors tend to be real hard to remove when cold.

The two metals being different will make it easier to remove when hot.

I had a guy at a shop ran remove the threads and all with the O2 Sensor
with a 1/2 impact gun for tires and a impact socket, after I had asked
him to heat the engine up. He knew to much and told me it would do it
cold after that I had to tap the hole and put a heli seat to hold the
new O2 Sensor