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:
ECU reset
(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.