What condition are the engine mounts and tranny mount in? It's possible that excessive engine movement from bad mounts is causing either the primary or secondary ignition to lose contact from a bad wire on deceleration.

Also check for vacuum leaks (hoses at the idle control valve are a prime suspect -- are they pliable or rock hard?) and for other vac leaks, and clean the air flow meter venturi.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!