The problem you describe is most likely the hose that connects the sensor behind the glove compartment. The hose is foam and disintegrates from age. It is very easily corrected.
Remove the glove box and you will see a pipe going horizontal toward the sensor that is below the small grille at the center of the dash. Use a piece of 3/4" foam pipe insulation from Home Depot. It works great for the application.
If once you remove the glove box, you find the hose to be intact and flowing correctly, post again and we will take you to the next step.