1.5dci glowplug light won't stop flashing.

I have a Clio 1.5dci from 2001 and after a recent visit to one renault official garage the glowplug light won't stop flashing. I delivered it back the next day and they put it on the computer machine and did something that fix it for a few hours. They said that to watch careful it it started flashing again.. wich it did the next day! :( THe next day the car was returned to the garage and it stayed there for a day, then they said it is the fuel injector.. I just took a run with the car and i notice that the car is running normally. So i got a few questions.. If it was the fuel injection wouldn't it lower it's accelerating performance? Could this be a ripoff? According to the manual it only says 'Electronic Malfunction'! Thanks for your help.