1995 Subaru Impreza WRX engine problem

Hi there,

My WRX has picked up a fault where it intermittently starts to fluctuate its electrical volts. The symptoms are most noticable when the headlights are on, they go from bright to dim, and when the engine is started you can hear a distinct whine (sounds like electrical interference), that moves in unison with the dimming of the lights. Also the car is not idling correctly, sounds like it is missing. And when driving if you accelerate quickly with high boost, the check engine light illuminates and the RPM becomes quite erractic, between 800- 2000 RPM. Any help greatly appreciated,

Thanks