Renault Clio engine management system

Hi, My son has a Renault Clio. It hasn't been driven often as he hasn't passed his test yet. Recently it has gone to the garage twice. First time the EMS light was flashing and the coil pack was changed. It then went ok for two short trips then started flashing again. This time it was the spark plugs, they were changed. Today, again after two short trips, it started flashing again! All times it has started to judder then has got worse and worse until you have to put your foot to the floor to get it going in first. Have I bought a dud or is there an underlying problem here? Any ideas welcome. Thanks.