Mate I've had the same problem,changed plugs leads and coil pack,and car was still like it.my mate came n pluged it in yesterday and cylinder 4 injecter was shown fault.easyest way to check which injecter it is is to keep the car tickn over at a grand,and unplug each injector one at a time and outing it back on.all the working injecters will missfire when removed the one that's down won't.job dun hope this helps
gary splitter, March 2016