Hi, My 02 protege es 2.0L has had the charge system light on for some time, and the voltage output of the alternator fluctuates up and down from 14 to 16 volts sporadically. It consistently does this at startup for a few minutes, then steadies out. At idle, this causes the rpms to fluctuate also. But you can hold your foot on the gas and bring the rpms to a steady point, and the fan, lights etc. will be cycling up and down.
Usually, after the initial startup, what will trigger the fluctuation is turning any significant electrical item on or off (lights, windows, fan etc.) So then the headlights are pulsing brighter and dimmer, the fan is going faster and slower... To correct it, you can switch any of these higher amperage accessories on and off about seven or eight times, and it levels out for a time.
I have had it tested at an auto parts store, it seems to be charging at normal voltage (around 14v). When the fluctuation occurs, it shows that the voltage jumps from 14 to 16, up and down.
Does anyone have any suggestions where to begin looking? I have tried pulling fuses to see if it has any affects on it, and it doesn't.

Thanks

 

My 2000 Protege has the same problem. Virtually the same symptoms. I have replaced the alternator and the battery. I have also tuned up the car. I still have the same problem.

 

I searched this out and replaced the alternator with a mazda rebuilt, but no good. After diagnostics, it seems to point back to the computer. A competent friend of mine pointed out that the engine in my protege is one that has been used by ford for many years, and that an older model alternator that doesn't rely on the computer for any part of its voltage regulation can be fairly cheaply acquired from a junkyard. This may not solve the battery light being on, but it will solve the voltage fluctuations, and I can live with that.
ya'akov