If your planning on keeping the car long term, it would be worth investing in a diagnostic cable. The regular VW OBD2 cable from Gendan for around £25 is compatible with subarus from 1998 onwards. You can download for free a copy of ECUExplorer which is an open source subaru diagnostic software.
EcuExploer displays realtime sensor information and fault codes, allows you to clear codes and reset ecu on the fly.
Its also easier to diagnose problems with lambdas and MAF sensors etc as you can see the voltage outputs from the sensors in real time. It also displays the maximum and minimum readings since starting the software. Once upto temp the lambda should see a peak voltage of around 5v and a minimum value of around 0.1v.
Its a good piece of kit to have, especially with Subarus, diagnosing issues with them is just a nightmare and can be expensive if your having to take it to a garage.
