1.5dci glowplug light won't stop flashing.

[DCBA]

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.