Check the Idle Speed Control Actuator. It's located under the air intake tube right near the intake manifold connection. If it's not reading signals correctly it will cause erratic idling. I'm thinking that when you decelerate the ISCA is allowing the throttle linkage to retract too much causing a stall. I have personal experience replace one on my previously owned '94 Eldorado. This is just a suggestion.
Here's a pic.
http://info.rockauto.com/getimage/ge...tex/2H1453.jpg