Yes, one minute fine and the next not working. It will cause the vehicle to run rough and misfire.
I concur!! Ive suffered two failures of coilpacks. One years ago on my brand new Ibiza cupra 20VT and a few months back on our Avant 20VT.
Was driving the avant stopped at traffic lights pulled away then the ECU light came on and it started running on three cylinders.
Luckily i was only 200 yds from Western VW at the time. So looked up their number on my iPhone called them and they had one in stock 10 mins later i was £30 lighter and running on 4 pots again.
The ibiza was running fine one day then the next day it started and was only running on 3 cylinders - Quick call to VW warrenty who dispatched The AA and the guy had one in his van.
I do remember at the time talking to the AA guy and him asking "This will be quite fast then? What does the APR Tuned badge on the back mean?" i Said Fix it and ill show you!!