2010 Subaru Forester Hesitation

Hello Everyone, fan of the YT channel so I searched there and did a search here. But I thought I'd post before I made a $200 mistake. After all the diagnosing I was certain it was a bad MAF sensor. But I tried a non-oem replacement and it made it worse. Subaru guys are telling me Subaru's are finicky with sensors and they don't like non-oem. So that's the next step at this point. 

The vehicle is a 2010 Subaru Forester X (SOHC). Here are the symptoms:

- Hesitation if I quickly press gas pedal, if I go slow it's far less noticeable.
- Idle drops and occasionally stalls if left in gear when coming to a stop.(*Edit)
- Gas mileage is really bad
- I'm getting a lean code P0171.
- I did the "unplug the MAF sensor" trick and the engine kept running only 1 out of the 5 times I tried it.
- Checked for a vacuum leak with TB cleaner and propane.
- MAF sensor was cleaned and eventually replaced with a non-oem brand as that was the quickest to get. But not only did the problem persist, the air flow rate dropped to 1.86 g/s. So the original went back in.
- Intake was removed and checked.
- TB was cleaned (It wasn't overtly dirty)
- EGR valve and hose was cleaned (Again, not that dirty).
- PCV valve was a little caked but still working. I had a spare so it was replaced. 
- No exhaust leak that i can tell.

Here is a screen shot at idle. You can see what happens the 3 times I pressed the accelerator:

Any help is appreciated. Thanks!

Was the P0171 set with the non-oem MAF reading 1.8 g/s at idle?

The present fuel trims are high negative may set P0172.

The P0171 was set by the oem maf. I only ran the non-oem maf for like 15mins because struggled to even idle.

This was just a sample. My trims can range quite a bit. It dumps a lot of fuel during acceleration and drops like a rock when I let go of the gas. It'll go up to +36% during acceleration and down to -30% when I let go. No P0172 though.

Here's a freeze of when it threw the P0171:
 

The screenshots are very much appreciated. 

Given the Freeze Frame and the data shot you posted, I think you're ready for an OEM MAF. The fact that it's overreporting at idle and (likely) underreporting under load is classic failed MAF behavior.

Technically, low fuel pressure/volume could also be suspect with lean trims under load. But, that doesn't account for the overreporting and rich trims at idle. Plus, checking fuel pressure on a Suby is a pain. I've also seen rare cases where a damaged/missing air filter was causing skewed airflow across the MAF. In these cases, the filter is obviously installed incorrectly or deformed. If you're in doubt, change it with the MAF.

If you wanted that 110% confidence, you could aways look at peak Absolute Load and peak MAF during a wide open throttle run through 1st and 2nd gear. I don't have known good values for this engine off the top of my head, but I'd expect 90% or more Absolute Load.

Thanks for the reply! I used to mod a couple forums back in the 2000's and something I held onto was, if a community is willing to help you the least you could do is try to give them a much info as possible.

With that said, I am an old school backyard "mechanic" just trying to keep the family's vehicles running, and all this is new to me. It's kind of like drinking from a fire hose. In trying to understand what peak Absolute Load is and if my reading was even accurate, I began reading your thread "Calculated Load vs Absolute Load". At the end of the thread you placed cardboard to restrict air flow and the Calculated load matched what I got in the Forester but then you did it again in a Ford Escape and it was back close to 87% Absolute Load. So now I have no idea what's going on, haha. 

In any case, I don't know how trusty these numbers are. Keep in mind this is all info coming from a BlueDriver Bluetooth scanner, as this is my first foray. My BIL has a Snap-On Solus scanner but has very little knowledge on how to use it. Plus it kept dropping communication suggesting to change Personality Keys?? Anyways. My Absolute Load at WOT was 58% and peak MAF at WOT was 56 g/s (I think. I don't think this particular scanner is able to record peak MAF, so I have to watch it while also trying not to hit anything and for cops. They are merciless here, the fact I'm reading it off a phone makes it 3x worse.)

Thanks again.

At the end of the thread you placed cardboard to restrict air flow and the Calculated load matched what I got in the Forester but then you did it again in a Ford Escape and it was back close to 87% Absolute Load. So now I have no idea what's going on, haha.

I totally forgot about that.   Had to go dig that post up. I think normally that Escape did 87% Absolute Load, but did 70% with the carboard installed. Calculated Load was 100% in both cases. Short version, Calculated Load doesn't do a very good job of highlighting breathing (or air mis-measurement) issues, IMO. Absolute Load is always the way to go, whenever it's available.

My Absolute Load at WOT was 58% and peak MAF at WOT was 56 g/s (I think. I don't think this particular scanner is able to record peak MAF, so I have to watch it while also trying not to hit anything and for cops. They are merciless here, the fact I'm reading it off a phone makes it 3x worse.)

Those values are terrible.     I still say go for an OEM MAF. Nothing wrong with the data you're gathering with the BlueDriver, either. As for peak MAF, I mostly just meant the highest value you'd see. I think the BlueDriver software will record that automatically in graphing mode:

 

SOLVED! OEM MAF sensor did the trick. That non-oem maf really messed me up and had me second guessing everything. I appreciate the help and the wealth of knowledge around here!