I recently got a new Coil Pack installed due to the engine misfiring, but now when Idling at traffic lights, round abouts etc, about every 10 minutes or so the car will vibrate and under rev for just a few seconds, this only happens when idling and it didn’t do this before the Coil Pack was replaced.

Also, after starting the car for the first time of the day, sometimes it will stall straight away, when starting for the second time it will start up properly. It's had this problem for a while now but it seems to be getting worse now.

Does anyone think the new coil pack that was installed is faulty? Or could it be another issue? I plan to take it back to the mechanic when I get the time. Thanks in advance for anyone's help