I had a similar problem with my 85 380. Does it stall often at idle? Does the engine surge and then die accompanied by an erratic tach reading? I replaced the ignition control unit (ICU)with fixed the problem. The ICU provides aan rpm signakl to the fuekl pump relay and tach. If this signal is compromised, bad things happen. The ICU on mine is to the left of the radiator inside the engine compartment,.