MAP Sensor
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 1995 GMC Vandura, 1995 GMC Rally, 1995 GMC Pickup, 1995 Chevrolet Sportvan, and 1995 Chevrolet Pickup. However, it is still accessible from the selected car via links, so may be relevant.
If control module senses higher than normal manifold pressure (low vacuum) system can go rich. Disconnecting MAP sensor allows control module to substitute a fixed value for MAP sensor. If rich condition disappears, replace MAP sensor and continue testing.