Ever since installing an electrical fan on my sported I've noticed a strange problem. My engine idols somewhere around 900 RPM and that this RPM I see the alternator outputs about 12 V. if I increase the throttle even a tiny bit too maybe 1000 RPM or 1100 the voltage increases to 14 V which is where I would expected to be anyway.

I'm wondering if this car would benefit with a slightly smaller pulley on the alternator that would make its been slightly faster when the engine is idle, or I'm not actually sure if my engine is even idling at the right speed does 900 RPM sound about right?

nothing wrong with the alternator or the battery they both are new and in fact the alternator is a high output alternator outputs I think 140 amps instead of 70 A like the stock one and it did this with the old alternator as well.

advice? has anyone else explored options for improving the system voltage at idle speeds?