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Whilst driving home this evening, my S4 shuddered a little whilst accelerating. Immediately the engine light came on, it sounds & feels like its running rough with loss of power.

I suspect a coil pack has failed. my local euro car parts has some listed about £33 each - so hope to pick one up tomorrow.
if I replace the coil pack will I need to reset the fault using vag-com or similar. I have an old version but not sure it will work (it worked on my old 25th Golf Anni) - I don't really trust it on my S4.

Is their an easy way to test which coil pack has failed, I read somewhere that fiddling with packs can also cause more to fail?

If you vagcom it you'll get two codes normally

Random misfire detected
Random misfire detected cylinder X

You don't really want to touch any other coil packs if you can help it and get ready for others to fail as well.

Worth getting a £40 fault code reader and keeping a spare coilpack and tools in the boot. Then you can swap them quickly and avoid fuel breaking down the oil

Your vagcom should be ok for the basics like this

Thanks Xyber -
could you recommend any fault code readers ? - will this allow me to reset any error codes.
I still need to find my old vag-com clone cable /ebay home brew. It defiantly sounds like one of the right banks (offside) is misfiring, but I have no idea which one.

I keep on of these in the car http://www.gendan.co.uk/product_GDVAG.html for basic quick check ups and have fully VAGCOM for in-depth stuff

That scanner has sub menus like engine, abs, gearbox etc for basic fault finding in a few modules. Has a reference code book and a code disc and is powered from the diag port itself and can reset the codes

After phoning around managed to find a specialist in Milton Keynes that could change the coils on short notice.
vag-com identified errors with coil packs 4 & 5.

Technician at DS Motors advised that the plugs also be changed as a matter of course.

Failed CP's :
Part Number: 077 905 115K
BREMI 12455ESM

- L2 A71D 6 15/05
- L2 A68B 6 15/05

Just noticed that visually the new coil packs are different to the originals. The old CP's have a flat head, whilst the newer type is slightly convex/recessed.

I think this might apply too mate:
http://www.rs246.com/index.php?name=PNp ... ic&t=89419

Thanks frustratingly this morning I ran into a another cylinder suffering a misfire this time number 8, I have just had coils & plugs on cyl 4 & 5 replaced. I drove straight to my local specialist and got all the remaining coils and plugs replaced. - pockets 400 Quid lighter
Ill give Audi a call to find out if there is any chance in reimbursement on parts. (cross fingers)

Good luck. Have lost 4 so far since ownership, 6 months.