Bah, I hate when I miss threads and have to quote 30 people.
I'd like to start off saying that I'm a huge fan of saying that an intake really should have a tune on the newer cars.
1.) By default, once you hit open loop fueling, it continues to apply a learning trim percentage fuel trim that was learned in a normally lower load range (depending on your tune, of course). The percentage does not apply evenly across loads. For example, at idle, you may need a 3% correction to get to a stoich mixture in eyes of the ECU. At wide open throttle (WOT), that 3% difference can mean the difference between 11afr and about 11.5afr. I know the car won't apply the trim learned at idle (low load range) to the WOT range, but the same issue occurs over the range of A/F Learning D.
2.) Boost response. I'm not sure of the effects of the intake directly on your cars boost response. I'd bet that the turbo is more responsive, and possibly at the limits of the ECUs turbo dynamics tables - meaning the ECU is maxing out it's boost correction ability. This shouldn't cause the "system lean" code, however.
3.) Slight differences between intake systems.. even with the same "MAF housing diameter". Every intake handles air a bit differently at various speeds. My KSTech intake (stock sized MAF housing) looked great as far as A/F learning & correction went at lower loads. It was in the 2.0+ load range where I started to see some fairly substantial variances from the stock intake. I may be able to kick up a graph somewhere or dig through for my scaling changes. For the record, A/F Learning D would never have picked up those differences since I would have been in open loop fueling long before that load range. This could cause a "system lean" issue.
4.) Everything else aside, the intake could have a mechanical problem associated with it. Boost/vacuum leaks aren't uncommon. Putting the MAF sensor in backwards is not unheard of (even though it doesn't in that direction I believe). If it is an oiled filter... the MAF could be oiled as well now.
Keep in mind, all cars are using a generic tune from the factory. Your car may have been at the very edge of that tune (for better or worse). The more you modify your car, the further you risk leaving that nice "generic" WRX that Subaru used to generate their tunes.
That being said:
I could see merit in that statement. I disagree the MAF scaling will be the same. Whether it is dangerously far off, who knows. It's easy to verify that with a wideband o2 and both intakes.
You can run the SF intake without a tune and it will be fine. But it provide no performance gains and be a just a noise maker until tuned.
Not every car is a like. Nor is every mechanic. For whatever reason, the OP had issues regarding his. Whether it was directly caused by the intake, we don't know, but we can speculate.
Do you have a wideband O2 sensor installed? If not, you cannot make this judgement. A "System too lean" can mean a number of things.
Yup. Especially in those load ranges. The narrowband sensor becomes useless once you hit boost.... which is where you start to care that your afrs are out of comfortable range.
And how does this mean a number of things? It's an in your face answer. It's a 2013. Not a 1993, what the hell else could it be???
Could mean various things. I'm not up to snuff with the "system lean" code, but for example, look at adding a high flow down pipe. That throws codes which appear to be "in your face answers"... when they really aren't. Poor catalytic converter efficiency could be triggered by having additional air passing the rear o2 sensor, as opposed to having 'polluted' air passing the rear o2 sensor. These codes are assuming a car with stock hardware. They are allowed to make assumptions when they build the car.
The SF absolutely requires a tune. I have a 2013 (purchased 9/28/12), and ordered the SF plus air box, Cobb downpipe, AP, and some other goodies....all in anticipation of OTS tunes. Got a little anxious, and after the 1000 mile break in, installed the intake just to see what I see. At around 4K, the car ramps up to a little over 17 psi, hits the overboost fuel cut, and stutters for a sec or two before it adjusts and picks back up (just like you're experiencing, I'm sure). The ECU is reading so much more air it has no idea what to do, so it cuts fuel and boost. Just stay out of boost, and it will drive fine, or do like advised and re-install the factory parts for a few more weeks. It took roughly 1 month for Cobb to release the first OTS maps for the 2012, so i'm anticipating roughly the same (though I really have no idea).
That's quite over confident, as stated. While I have my opinions on the matter, these cars always manage to surprise me somehow.
You'll know when the ECU is reading too much air though. You'll get a "MAF sensor" OBDII code... showing you pulled 5V on the sensor. You won't hit that with an intake unless you've fouled up the MAF sensor. Which I have in my experience. Every time it rained or I got my car washed and hit boost that'd happen. Otherwise... the ECU will use it's highest load range values for timing/fueling/etc when it runs off of the table in the tune. You shouldn't be running that far off the table for it to make a huge impact.
Over boosting is a legit issue though. I thought whenever it through a fuel cut of any sorts you got an OBDII reminder, however. Tuning a catless car with the IWG makes you very familiar with this OBDII code. There are some 'soft' boost cuts to my understanding. If you pick up X amount of detonation, the car will pull boost to the best of it's abilities (normally 7 psi). I don't know whether a detonation invoked boost cut throws a code.
I see this stated with absolution, feeling your confidence, and yet I see no supporting data. So lets dispense with the opinions and accept this entirely as speculation. Now, if someone with a 2010+ (Shawn Mangan to the front please) would please load the Stage 1 map with Stock Airbox and Stage 1 map with SF intake and lets have a look at the MAF scaling.
Correlation =/= Causation
I will dig up an example of my KSTech intake vs the stock if I can find it. They claimed it didn't need a tune due to the same diameter MAF housing. It did. Cobb I am sure put in some additional engineering time though.
I wish no manufacturer would claim that their intakes are "stock tune safe". Stop wasting engineering time on them... put a tube with a smooth MAF curve together.. and sell it for cheaper. You really should get a wide band o2 once you start altering air/fuel values in a car outside of manufacturer specs in my opinion. You are a blind man otherwise.