VW golf flashing engine management light, loss of power??

I have a mk4 1.4 golf and as i was driving along the other day i suddenly had a loss of power and the engine management light started to flash. I have changed one of the coils connecting to 4th cylinder as i thought originally that was the problem but the problem still persists. I read that you may hav to drive the car for 20 mins for the ECU to scan the car again. Cud this be all i need to do?? HELP PLEASE???