lol had one to fix last time i was in uk!!
know the owner, and a lot of people had told him to replace the coil pack they are known for problems< so he did, and it made no difference, he could drive it ten miles and 200 miles and it would do it very randomly, engine light came on and power died, he used to stop turn engine off and wait 5 mins then it would start and drive no problem till it went again,
it had "multiple misfires detected" according to the codes, knowing the head gasket was replaced the previous time i was on uk
so about a year old, I did the following,
new fuel filter
new air filter
new plugs, cleaned the stupid breather system,
then added a can of forte fuel system cleaner to the petrol in the tank(about a quarter)
went to the m40 j9, headed north to j10 at 6000rpm in 3 rd gear, :-Xcleared all old codes
filled tank with optimax,
used it for a week and not one problem, emailed him last night and he said its running fine no problems its now done a couple of thousand miles since this and so far the problem has not returned
NB before the head gasket was changed it had a problem with using oil, it could go through max to minimum in 500miles, searched around on the net and it appears that the headgasket was to blame, I personally think it was to do with the breather being blocked owing to long service intervals, as couldnt find a lot wrong with the headgasket to be honest