Newbie having Dam issue

[dakota1221]

2015 WRX 59k miles stock except access port and cobb stage 1 tune
I've had the car about 6 months a couple months ago it started running rough (looking back I realize the dam had dropped) so I checked for a boost leak cleaned map and maf sensors and did an oil change spark plugs and air filter that didn't fix it. I then bought an access port to hopefully monitor and diagnose the problem. When I installed the AP it flashed the ecu and the car went back to running normal

a couple weeks later the dam started to drop lowest it hit was around .325. I tried fresh gas and it didn't go when that ran out tried fresh gas again (Shell 92) and 3 gallons of e85 then re-flashed the tune. its been a little over a week and dam dropped again to .500 highest i ever saw fbk go since the last flash was -2.8 but fkl hit -5 once and hits at least -1.8 whenever I enter boost

So if its not bad gas and not the ots tune (since the issue started on stock) then what do I need to look at to diagnose and fix the issue. What do I do

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[moisleg]

Consider a pro-tune by a reputable tuner who can analyze logs in-depth and tailor the timing/fueling specifically to your car.

Sprunki Game

[Unabomber]

REPLACE your MAF, its time and they go over time. If that doesn't work, then its time to find a local/regional professional as it could be a mechanical issue.

[Charlie-III]

Every time you flash a map, clear CEL codes, or disconnect the battery, the ECU loses "fine learning" and reverts back to baseline values in the map (aftermarket tune or OEM). This means if it's learning an issue and runs poor, you clear that and it starts learning again.

[Brock31]

Since you have the Cobb AP, and are able to data log, I would log and see if you're getting misfires.

Also check AF learning. That can sometimes be a good indicator if you've got a boost or vac leak because you're fuel trims will be all screwed up.

[CarticuS]

i would really look into a pro tune, i had a cobb OTS on my 2019 wrx and found i had nothing but dam fluctuation even though everything was clean, new, well maintained. before i got a Pro tune from Mach V i had a stratified tune just to see me through and didnt have a single dam issue for the 3 months i was running it before the pro tune. I appreciate that cobb is the benchmark but ive found that unless you have all cobb, its not that great, especially if using a Cobb intake.

Sine all that ive done a USDM to JDM swap and had the pro tune by Mach V and never had a problem with dam. But also the guys at Mach v told me that on the FA, the dam drops are not as concerning as they are on the EJ's.

Lastly, best thing i did was take the dam monitoring off my AP as the slightest drop would drive me insane and with cars that are so sensitive to AF, fuel its gonna happen.

[cmiovino]

I think it's a mechanical issue.

First, don't just be buying an Accessport and thinking flashing a stage 1 tune is somehow going to fix "running rough". Running rough sounds like a mechanical issue like a boost or vacuum leak, bad gas, bad MAF, etc. Tossing on a tune doesn't fix the issue.

Just looking for vacuum leaks might be enough. It's best to get smoke test done at a shop to really see. If you can definitely rule out leaks, you can then start looking at or replacing MAFs, front O2 sensors, etc. I take the stand MAFs generally should last longer than 59k and probably need replaced closer to 100k if you're cleaning them, but hey, it could have failed early. Smoke test first.

If you can't figure it out, I'd get it into a Subaru specific shop and a knowledgeable person run through their diagnosis. No harm in that. Cheaper than buying an Accessport.

[Front_Plate]

COBB stage 1 ots is pretty agressive with timing from what I remember. Was constantly seeing dam drops before i went e tune. Id suggest getting a professional to tune your car.