[shorod]

Thank you for the follow up post!

The alternator supplies unfiltered current to the charging system. The output from the alternator can be quite noisy and by design will have a multi-phase (typically 3) alternating current (AC) fluctuation. Electronics don't like noise. Noise can cause logic level transitions in high speed electronics as well as cause what appears to be low voltage to the electronics. The car battery acts like a large capacitor and filters the noise and AC in addition to storing A LOT of charge for the high demand, low engine speed situations such as sitting at a stop light with the brake lights on. Other high demand situations would include the A/C compressor clutch kicking in and loading the system in addition to the IAC attempting to speed the engine up, etc.

-Rod