Car problems Seat Ibiza?

Been having problems wih my 57 Seat Ibiza 1.2 inj, Engine Management light came on a month ago, took it to garage they did a diagnostics on it and they said it was coil one missfireing, replace all 3 coils and sparks and worked fine, last week engine management light comes on again and it looses power making the car very sluggish, turned engine off re started and worked fine until a little further down road and it lost power again. Took it to another garage to have diagnosed and he thinks its a fault with the ECU connecting with Cylinder one, he says all coils are fine engine is fine just that when you start the car up you get a perfect signal car runs fine, as soon as you rev the engine for less than a minute all signal is lost and car becomes sluggish and looses power. He has advised to have the ECU sent off to be tested, anyone else had this problem? and what was the outcome? i know im prob looking at alo of money to get it sorted just weighing up my options. Another question if i got another ECU from a salvegers matching my cars engine would this run my car ok or is it not recomended?