So, for those who had the patience to read through my pain, ehr.. posts, here's the final update. Unfortunately after my last post the car went back to the same issues and even worse.
I am going to write the full story here, more as a personal journal than actually because I believe there are people interested out there
Note: I will let the numbers talk as all the info in here are backed up by dyno charts (see bottom of the post) [2][3].
Chapter 1: My car before
It all started with my car being happy. I did only RJM clutch, clear bra and tinted windows when I decided to get new intakes. I looked around and pulled the trigger on the AAM CAI. These intakes, as many of you know, come in two
modes and, since my car was stock at the time, I decided to leave them in S-Line. I have to admit, those intakes in S-Line really impressed me, and I also wrote a very positive review about them [1]. Up to here, green light, all good, butt-dyno was telling me the car gained some little power in the mid range, and the sound was good too.
Chapter 2: The new mods: the good and the bad
Finally the day of my Fast Intentions CBE and HFCs arrived! Oh, joy, I had already planned a tune so I decided to go ahead, change the exhaust and remove the CAI restrictions, switching therefore to R-Line mode. I have to say that I am at fault here as, to remove the restrictions, I scratched them and decided to toss them. This was a BAD move.
On the first engine start a bright CEL came out but I didn't really care about that... I mean.. I was getting a tune so that should've fixed it. So I brought my car to the tuner and after a day it was ready. The dyno chart (Dynojet) was looking good, car definitely was doing +20whp from the stock baseline. I left, drove around a bit and went home. The next morning, when I started the car my happy face frowned. Car was lacking almost all the power, no torque whatsoever and the CEL came back. So with a buddy of mine, we checked which code the ECU was throwing:
Code:
P0101: Mass or Volume Air Flow Circuit Range/Performance Problem
P010B: Mass Sensor B reading
So I brought the car back to the tuner shop, the car was running super lean and the ECU, on a cold start, was falling back to the cold map (stock-ish like) and not reverting to the original. So, based on Uprev's advise the tuner copied the tuned map over the cold one, so no matter what the car would've used that. I've got to say every time I was leaving the tuner shop, the car was doing good for a few hours. Anyway, that didn't solve the problem.
Now, also, the car was behaving oddly. On a cold start, the car was experiencing lack of power but if I drove around for a couple of minutes shut off the engine and turned it back on, that had its power back. Notice that CEL never went away and was coming back after clearing it. Also, the "power" I'm referring to had a different feeling that stock, it had a sort of tiny lag when going WOT and then rev up. So, again, not good.
Chapter 3: MAF scaling tune
At this point, my tuner (and I first) called AAM and Uprev (again) and he started testing the car with different MAF values as suggested by AAM. He kept the car for a couple of days but the car got even worse. So he flashed back the original tuned map. It's a pity we couldn't get the tune right, but that would have probably required too much time. My Z is my DD, I use it to go to work and even leaving it at the shop for a full day is difficult.
Chapter 3: The solution
At this point I had to make a decision on what to do and, despite my happiness with the AAM product, I pulled the trigger again and got the Stillen Gen3 intakes. My tuner offered me to re-dyno-tune the car for free, so I went that route. I can only say.. WOW! The new intakes and the new tune got me back the perfect N/A feeling the car used to have and made even +6whp (compared the previous tune) [3]. Now my car feels just "awesome".
There you go Josh@Stillen 
another super-happy customer for you.
Acknowledgments:
Props AAM and Uprev for assisting with the problem and a huge thanks to my tuner Rob @ Z Car Garage in San Jose, CA.
Pictures:
References:
[1]
Review: AAM Competition Cold Air Intakes S-Line/R-Line
[2] AAM CAI Dyno (compared to best run in baseline) - MAX 318whp
[3] Stillen G3 Dyno (compared to another run in AAM) - MAX 324whp