why do my car just die down and cut off while i am getting ready to stop or turn

Did it do this before the air filter replacement? This happened to me one before and it was caused by incorrect ignition timing. Yet a faulty Throttle Position Sensor, Mass Air Flow senosr or Manifold Absolute Pressure sensor can also be likely culprits. I wold look for a damaged or disconnected sensor near the air cleaner/intake.

if it has a mass airflow sensor I would tap the sensor with a small hammer while the car is running if it stalls then you will need a new maf