Newage Impreza diagnostics

I've got a 2006 n/a hawk Impreza. I've recently developed a power loss and jerky power delivery between 2 and 3000 revs. 1st garage I went to couldn't get any error codes, my diagnostics couldn't. They got a specialist out, and found old codes for an 02 sensor and an injector. Told me to drive it and see which codes come back, but the codes haven't come back by last week. Then I read on another site that elm327 chips don't work well with Subaru's

(http://www.subaruoutback.org/forums/65-parts-accessories-performance/39426-freessm-complete-access-your-ecm-tcu.html#/topics/39426),

so I now have a vag-com cable with a ftdi chip and tried freessm by berios, still no fault codes. Any recommendations for diagnostic systems? I'm a bit puzzled why the engine management light wasn't lot for the old codes, too.

(It's currently having the 02 sensor replaced and an injector cleaner through as a precaution, although not sure if they are the problem)

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