Lambda Sensor

[evokiller]

hi guys my car has been running like ##### for 3 weeks i replaced a broken lambda sensor 3 weeks ago for a new subaru one but it started to hesitate between 2/3 grand and got worse when it was raining but last night i disconected it and he car was running brilliant reconected it today and the car is back to hesitating so it seems to be a faulty sensor i think but there is no cel light or code comeing up i phoned halley and they said theey would need to put the car on a diagnostic but would just look for error codes so i told them there were none but they insist on it but i am not paying them more money just to say nothing is wrong its there sensor aswell any ideas as to what i can do about this cheers evoki ller