I don't actually want to be here, but... my vehicle qualifies. This is the first time I have posted about this despite doing as much research as possible.
I have owned a 2005 LGT 5MT for about a year now. Purchased in Florida and transplanted up into Ohio/Michigan area. I didn't notice the stutter/stumble when I first got it, no CEL either. Over time it has progressed to a point that I was/am sure that there was a true intermittent misfire occurring. The owner stated all maintenance was done at a Subaru dealer, and there was papers to prove that. Stage 2 parts and tuned, supposedly. With 15 psi max. It is my first turbo car so it was a fair amount of adjustment.
The stutter was getting worse and I was fed up. Purchased AP v3, installed over the weekend. It discovers it has a Cobb tune on it already. I install the Stage 1 tune that similarly runs 15 psi; I'm trying to be cautious, right? I'm aware of the ringland problems and fear the worst. So lets get into it, I guess..
TYPE OF STUTTER/STUMBLE
Steady throttle/Increasing throttle/Both: Steady throttle, very minor increase
MODS
Intake: Stock
Exhaust: Stock
Other: Aftermarket header, catless up pipe, down pipe
Fuel: 91
Turbo: Stock?
Engine Management: AP
Tuner and revision of tune(if you don't mind): Stage 1 Cobb
MAINTENANCE
Sensors changed: None
Plugs changed: None (but soon to come)
Coil Packs changed: None
Other: Cleaned MAF, it was super dirty, nearly impossible to get clean, checked yesterday, dirty once again
OTHER SYMPTOMS
Check Engine Light: Yes, P0303
Etc: and EGT?
RESULTS
What has and hasn't worked for you: MAF cleaning
If something worked, how long has it been working for: N/A
To continue (I know this is long), since installing the new Stage 1 tune and clearing out the previous map, the CEL now comes on with a cylinder 3 misfire after driving under certain conditions (see next paragraph). Not really surprised. Whenever I felt the stutter/stumble I thought "that feels like a misfire, but no CEL.. what the hell." Now I have somewhere to look and datalogging capabilities to assist.
However, I am new to this datalogging thing, but I want to learn what is necessary to be successful with it. I have found cylinder 3 has recurring knock and roughness. Significant under 0.55 load and around 2000-2500 rpm. Not to say it doesn't occur under similar load around 3200, but it is less severe and less frequent in occurrence. And at times at idle under hot conditions.
So, I will be compression testing (oh god, fingers crossed) and changing plugs, checking results. If not successful, swapping coils. If not successful, swapping injectors..