2001 ej20 etune - losing power at 4000rpm

[JamEj20]

so recently purchased a 2001 legacy ej20 e-tune 5spd manual and everything was running fine until a couple days ago. 1- check engine light has been coming on then turning off at random times  mainly when idling for longer period of time . 2- so car drives fine and normal with no problem until you want to hit accelerator and take it up to around 4k rpm then it starts to shake and just refuses to climb any further until you change up a gear then does the same thing until your in 5th. once in 5th if you just slowly increase  the acceleration then it will pick up speed and cruise fine at 150khms (not actual cruising speed I follow the rules ha sometimes) . no funny sounds no leaks I can see and no other problems. just scaring me bit as to hoping its nothing major. I'm thinking maybe fuel related and not turbo related but would love some input. located in Otago and am keen to find good reliable Subaru techs for future mods if anyone has some recommendations .

[thewabbit1]

could be knock sensor. have you had the codes pulled?

[JamEj20]

no not yet thats the next thing I'm having to get checked. just bit strange aye , just yeah going up hills around Dunedin its struggling abit. could be any couple of things hard to pin point. 

[thewabbit1]

once you know the code its pretty easy to narrow it down

[Andy_Mac]

Probably something to do with the secondary turbo kicking in if it drives fine up till 4k. Probably crap in the lines in the BBOD causing something to not switch over. Get the code checked rather han just taking a stab in the dark though