Hi. I am a newbie to the world of Subaru having
only recently bought a 2004 plate 2.5 Sports Tourer. Within days of buying it
the engine management light came on and I thought it might be helpful to share
my experience. The car was also runing rough in lower gears and threatened to
stall when slowing down at roundabouts etc. A very helpful auto electrican did
the diagnostics and it was the front o2 sensor that was identified as the
problem. A Denzo sensor was fitted but still the problem of the light and bad
running continued. He recommended I take it to a Subaru dealer which I did.
They identified the same problem and tried their own aftermarket sensor - no
improvement. A Subaru own sensor was ordered and this time it did the trick -
no more engine management light, no bad running - all running beautifully. I
thought this might be useful to others who come across the same problem. 

Hi mate welcome to S.O.C 

And thank you for sharing the info that I'm sure will help other's. Can't believe how much trouble the one sensor did. But least you have it sorted now :) hopefully help anyone else 

Wotcha and welcome - great first post, very useful to know... a demon second post might be sharing some photos of your scooby ;)