Replace the PCV Valve.
For my Mazda I use 10w-30
yes all cars do .
A 2001 Mazda Protege uses standard 10w-30 motor oil. This provides a good balance of viscosity and protection for the engine.
Look at the rear or side of the oil pan
4 in a 90-94
I am sure it is 3.9L
For a 2002 Mazda Protege 5, the recommended oil is a 10w 30. 5w30 is recommended in temps below 30 degrees f.