I have the MPX4115AP sensor. I have it hooked up according to you datasheet. The output of Pin 1 (Pin 3 is +5V) starts at 3.8V when power is first applied, and then drops gradually to about 2.5V after 5-10 seconds. The air pressure is not changing.
When I do change the air pressure, however, the reading continues to drop - it has no effect.
Any help would be appreciated (and the sooner the response the better)!