Coil replaced, engine still misfiring?

Hi, I have a 2001 Toyota Yaris and the engine management light came on last week. I took it to a Toyota dealer and after investigation they replaced the 4th coil pack.

Since then, I've noticed that when accelerating at speed, especially up hill, it sounds like it's still misfiring, although the engine light hasn't come on.

I can't believe it's just a coincidence that this has happened so soon after the same problem was fixed. I'm going to take it to the garage next week but I don't want to be conned as I already paid £200 to fix the original problem.

Any ideas?