Manifold Absolute Pressure Sensor

The engine's computer system can make the engine more powerful, economical, and smooth if it can accommodate for changes in air pressure within the intake manifold. The MAP Sensor, or Manifold Absolute Pressure Sensor measures this vacuum by measuring its pull within a neutral area of the intake manifold, after the throttle body (behind this due to the pressures which change when it is closed).

Most MAP sensors on naturally aspirated can only detect low pressures, since that is all they encounter.

Sometimes, when an engine is upgraded dramatically (often the case with forced induction), the original MAP Sensor needs to be upgraded too, so the higher and lower pressures can be properly detected.