O2 Sensor Wire
WARNING: This page is about a different car, the 1990 Chevrolet Corsica, 1990 Chevrolet Cavalier, and 1990 Chevrolet Beretta. 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.