Bringing this topic back up as I search through the forums here. My car is dipping to 500 or below only when I'm at a complete stop. Even when starting it, it stalls out from time to time. I've taken it to Nissan twice in the past 2 weeks, and what they thought was just some cleaning around the throttle body and fuel injectors didn't seem to be the solution. I have no idea why they can't figure this out.

I do, however, have a Stillen G3 installed and I'm wondering if it has something to do with that.

Any way, has anyone ran into this issue lately and/or has found a solution for this?

i had the same thing, dip to 500 then stumble and back up to 650ish - had the Stillen G3 too. it was one of the fresh air feeds for the crank case ventilation system. I cant remember which side of the Stillen piping though, but if you have digital calipers measure the inside diameter of both fresh air feeds and you'll find one is smaller than the other.

The fix is to saw the small one off, enlarge the hole to suit and weld a new bung with the correct inner diameter onto it. You will need to really wrestle the hose over the new bung though - for some silly reason stillen didnt give reinforced hoses for the ventilation system so they will tear if you aren't careful.

I am having exactly same problem. Just cleaned mag sensor but didn't work out. Any one who can help me with this?

Had the same RPM dip together with slight batter voltage drop when rolling to a stop at neutral (idle drops from 650ish to almost 500 RPM) (mine is 6MT). After a month of trail and error I finally fixed it. I though of sharing my process of elimination.
The RPM drop happened about 3 out of 10 times back when my car was completely stock, but I didn't bother to fix it. Then the problem worsen after I replaced the stock intake to Stillen G3 CAI. It happens almost 90% of the time and I finally decided not to be lazy and treat her right. Thanks to Z family's posts I listed the potential causes and rearranged them in the order of least to most workload:
1) Gas: I used to getting gas from Costco. So I switched to Chevron. Nothing changed after 2 full tanks.
2) MAF sensor: cleaned it throughly and still nothing changed.
3) ECU reset: I thought the RPM drop might be caused by not resetting ECU properly during my install. But i don't want to go thought the hassle to reset power window, radio, service reminder... list goes on. To avoid all that, this is what I did. Most people have seen the crazy "cheat code" and here is one example: http://www.the370z.com/nissan-370z-o...ecu-reset.html
(post #6 by cdoxp800). Tried it but still nothing changed.
4) Throttle body: I was trying my best to avoid this since my CAI requires me to take the front bumper off (yea, once again being lazy). But with options running low I ended up cleaning the throttle body. I used this as my guide: DIY Clean your Throttle Bodies - MyG37
I was surprised how dirty mine are for the millage I have (45K miles). Got lucky and problem fixed!!! Now is day 3 since the fix and haven't had RPM dip with or w/o AC on.
5) O2 sensor or MAP sensor: luckily I got my problem fixed by #4. Otherwise I would of gone through the hassle to put the stock on and take it to the dealer hoping whatever they can find will be covered by warranty.