peugeot 206 1.4 feels sluggish

[MARKS6900]

Hi, car was running fine yesterday but today it felt as if it was only running on 3 cylinders, took it to the local garage who plugged there lap top into it, it came up as number 3 injector not working, so they took of the injector rail and cranked it over, number 3 was working but number 1 was not so they replaced it, car runs fine at idle but as you accelerate it seems to be sluggish, i have rechecked all the parts he touched but no difference, any ideas, thank you.

[MARKS6900]

Hi replace spark plus, job done, runs perfect now, thanks.