Differential Pressure Feedback Electronic (DPFE) Sensor
WARNING: This page is about a different car, the 1995 Mazda B4000, 1995 Mazda B3000, and 1995 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.
DPFE sensor should set a diagnostic trouble code. See appropriate articles for code retrieval procedure;