Why would my car be dying when slowing down or stopping.

The key to this problem lies in the disconnected battery. Basically, disconnecting power from this model basically wipes out some of the stored settings on the ECM (Electronic Control Module) or on board computer. This model is required to be taken to a dealer or repair facility to have the ECM connected to a T1 controller to have the Idle function "re-learned" otherwise the car will never idle properly. I own a 1991 Corsica with a V6 3.1 and battle with this problem all the time. If that doesn't solve the idle problem you could have a faulty Idle Air control sensor. It's connected somewhere on the throttle body and has a wire connector on it. Hope that helps