Random rough idling, getting worse

I agree sounds more like a coil pack to me.

RockmanRock wrote: I would have thought a position sensor failure would cause bad idle across the board, not just when cold? And the change of plugs did fix it for a while. Although I suppose it could be the heat getting to the cam sensor...

Usually happens when the sensor heats up.

Ive been driving at 70 mph and all of a sudden things have give very erratic.. stop for 5 mins, restart and proceed at slow speed noproblem.
Changed the sensors, (wasnt sure which one it was) and the problem went away.
Coilpack sounds a good candidate though

Thanks for the feedback all, hopefully the new coilpack will turn up today, so I can do some swapping over the weekend and report back.

Sorry for the delay in posting resolution, haven't had much spare time to get it done. Anyway, swapped out one coil and it still played up, so swapped the other instead, and problem seems to be gone (only test drove for about 3 hours so far, but was coming up within 45min before). FYI, tested the resistance on duff coil, and it was within the specs in the workshop manual so no obvious clues. Tried replacing the rear one first (thought it may have been the more likely to wear out due to heat) but it ended up being the front.

Got round to checking the bad coil more thoroughly; after pulling off the boot, had two hairline cracks as can be seen in the image. These were missed before, as they were hidden under the boot rubber. All that trouble from two tiny cracks

Glad you got it sorted!
My nephew was quoted £1200 to replace the engine on a polo after he had had a mess.
Symptoms were missing at idle and after 10 15 mins.
Lumpy running and cutting out.

They told him it was his cam belt had jumped a tooth and caused internal failure that was not at that stage catastrophic!

One second hand coil pack later and it ran as sweet as a nut!