O2 Sensor Wire
WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 1990 Pontiac Grand Am, 1990 Pontiac 6000, 1990 Oldsmobile Cutlass Cruiser, 1990 Oldsmobile Cutlass Ciera, and 1990 Oldsmobile Cutlass Calais. However, it is still accessible from the selected car via links, so may be relevant.
O2 sensor wire may be mispositioned and laying against the exhaust manifold. Check for ground between sensor and wire connector.