Wavering Idle and Dropping Voltage

earwicker7

I've been having a weird problem over the last few weeks. First off, there have been a few times where the idle wavers. Both times that it has been really noticeable, the oil temp was around 220, which isn't out of line to the best of my knowledge... I was driving fast, but not abusing the car. I pulled up to a drive-through, and while in park, I noticed the idle wasn't staying constant. It would go back and forth between 700 and 900 rpm, switching every second or so, almost like someone was tapping the accelerator in rhythm. This was only in park... if I kept it in gear with the brakes on, it stays constant at around 600 rpm. I was due for a 3 month service, so I went ahead and had them look at it... of course, they found nothing (they never do lol).

Anyways, that was over the weekend. I don't know if this is related, but starting yesterday, when I come to a complete stop (not in park, but just using the brakes), I often notice the voltmeter dropping from 14V to 13V. It only happens for about a second after I come to a stop, then it goes back to 14V. This has never happened before yesterday.

Does anyone know if these two are related, and what it might be?

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2009 Magnetic Black 370Z with Touring, Sports and Navigation Packages--Fast Intentions CBE with 12" Resonators/Carbon Fiber Mufflers and LTH--Stillen G3 Cold Air Intakes, Underdrive Pulley and Grounding Kit--Uprev Tune