I also have the same problem w/ my engine. (Sentra 1991 super saloon 1.6)
1. When I accelerate hard, there's a ringing sound in the engine.
2. When I lift my feed of the pedal, namamatayan ako as the engine loses rpm. I have to press the accelerator pedal pa while braking.
3. Hard starting in the morning. Have to press the accelerator pedal to start.

Any ideas? Mechanic just adjusted my idle up. He says to observe it for a week. Pag bumalik problema, I have to change my computer box raw...(mahal)...