You need a code reader to find out the fault code.You can get a cheap obd reader from Ebay for about £20.Should tell you exactly what it is.

http://www.ebay.co.uk/itm/Car-fault-...item35b37c476c
If it is coil pack you should be paying about £30 for a non genuine one.
You still need to erase the engine management light even if you do fit coil pack and it cures the problem.
My advice ,get the code read first or you could be changing everything.