2010/2011 Legacy GT auto, lurch/bang at low throttle when cold

[SpidersWeb]

Hey guys, wasn't sure where to ask so thought I'd stop by and see if you guys can point me in the right direction. Hopefully I put it in the right area.

I'm in Wellington. Car is a 2010 (2011 model, but registered as a 2010) Legacy GT 2.5 automatic from Japan, 124,000Kms. I'm the first NZ owner, so no maintenance history and I still can't work out how to set my clock. I've had it for almost a year and over this last week when I leave work (CBD) if I go from mild (5-10%) to almost no throttle, I hear the engine revs go up a little (but not travelling any faster) and then a very loud bang (which kind of feels/sounds like it's coming more from the mid/rear of the vehicle than upfront). Reminds me of a learner driver dumping a clutch.

Engine sounds smooth the whole time. 
Car is generally very quiet and smooth.

Once it's done it once, it's good for the rest of the trip. But it did do it to me a second time on yesterday's trip shortly after leaving a petrol station (so was shutoff for 10 minutes).

Doesn't do it immediately  - I usually exit the carpark building and drive ~50-100+ meters before it happens.

Doesn't do it in the mornings when I leave for work. (less traffic + 70 zone, slightly different scenario).

If I'm careful with the throttle, e.g. holding it at a set point rather than accelerating then lifting off, I have managed to avoid it once in the last week.

Due to time issues, I've mostly given up being a DIY mechanic now days, but hoping to get some insight/thoughts so I can make some decisions on where to take it or what to ask for.
I've been ringing around and Hutt Automatics was recommended, but they're backed up until October and not super convenient for where I live/work. 

[sobanoodle]

Rough gearbox down/upshift? 

Mine (2010 GT) was getting a bit rough at times in busy Auckland's traffic until I had the transmission control unit re-flashed/re-learn procedure done - pretty much fixed all the issues. 

The only owner before me (NZ new) mostly did open road and I guess the TCU adapted to driving in those lazy (for the gearbox) conditions.

 

[SpidersWeb]

Cheers for the reply. It's hard to describe it as a rough shift although I guess it is really, but its quite a loud bang! But I like the idea of getting the reflash done, as I paid a bit more attention this morning and noticed when I drive in the morning it kind of sits in gear - where as in the evenings it's always hunting between gears in traffic even when cold.

 

I used manual mode when I left yesterday and completely avoided it, once it warmed up I popped it in drive and it was fine. 

 

I also noticed in the mornings I use more and consistent throttle - and it changes to 2nd quickly, where as in the evenings in CBD traffic it's a very slow shift.
 

My plan at the moment is to get the fluid/filter done for piece of mind, then I'll see about getting a reflash/relearn done. Where do you go for that kind of thing? Is it dealer only or specialized or most mechanics?

Edited September 6, 2017 by SpidersWeb

[sobanoodle]

You need appropriate software/firmware for a reflash, I'd say only Subaru authorised service centers will have access to that. Had mine done at Winger Sublabs.

Get a reflash done first as it's cheaper, then do a fluid/filter change (the filter is inside the oil pan on these).

 

[duncanm]

rear diff mounts rooted?  Easy to inspect