whats up with the mini ..

[Donboy]

Its a 54 plate cooper that goes great most of the time , but when you stop at traffic lights for any more than a couple of minutes it shudders and runs ruff ,but if you switch it off then restart before setting off , its fine,,,
I've replaced the plugs , coil pack ,and bought a code reader that always says misfire on cylinder 3 when I check it ,,
I've swapped the plugs around ,,
What next ??
Any ideas??

[helix402]

You could try swopping the injectors around.