The engine control module (ECM) electrical grounds on the front of the engine block may have high resistance causing a rough running engine or stalling condition.Google+
Car Problem Reports
Cadillac Fleetwood Performance Issues Due to Faulty ECM Grounds at Front of Engine
Cadillac Fleetwood Problem
Visitor, 1991 Cadillac Fleetwood, 140,000 mi
Runs fine, the all of a sudden, begins to run rough, rough idle, stalls when stopped or in turns, check engine light comes on only when on highway, sevice soon light on sometimes. 2 different mechanics couldn't find problem.