When decelerating engine dies, please help?
 

1). For the last two weeks I've been having problem keeping RPM around 500 in slow speed, especially when suddenly decelerating to a stop, the engine dies. I am forced to constantly shift from D to N to keep the car running. 6 months ago I've changed ignition wires and cap, but not a rotor (screws were worn out). Could this be a problem? Also about the same time ago I had my fuel pump repaired by Mercedes dealer. Since than, the car sometimes chokes especially in high speed. 2). After driving on the highway around 70-80 mph for 30min. and slowing down to let say 30 mph, I smell antifreeze. What's up with that? No visible leak! Please help me out guys; I'm new to this forum but already love it.