I'd do the fault code check yourself. (
clicky)
The rolling road isn't going to help you unless you're looking to change your ECU. Well, I suppose you could use it to find a safe boost level rather than road tuning... The point I'm trying to make is that the standard ECU is not adjustable; you need to get a daughter board fitted to it (or have it replaced with something else) if you want to go mapping it on a dynometer.
I see you've already asked Ed about his services; he's got a good reputation, but if you want to remap the car I think he'll sell you a Nistune board. - I'm not sure who or what else is in your area.
I'd still check the new leads and cap; you've got to ask why they were put in... did it already have a missfire and the previous owner thought this would fix it? Did someone erroneously believe that having pretty coloured leads is an upgrade, and have introduced the problem? Has someone put new plugs in with the new leads and cap... and not gapped them correctly?
I'm not trying to be all negative, and I wish you good luck.
I guess what it is, is that I don't like to see people thinking "it's an import" or "it's turbocharged so I can't take it to a normal garage; I need to take it to a specialist"... then they end-up paying for things they don't need because so many places just replace things instead of fixing them these days.