Sorry for the rather long post but i thought it best to give the whole history of this problem so far:
My S3 has a misfire on cylinder 1 which is causing the CEL light to come on, When i scan it with vag.com it reports codes 016684 & 016685
016684 (as i understand it) is the general misfire code which occurs whenever any cylinder misfires
016685 is the code showing the particular cylinder that is misfiring (cylinder 1 in my case).
It's really noticeable if the engine is cold, when i first start the car, the revs are at 1200rpm and it's not too bad, as soon as it drops to it's normal idle of 800rpm you can feel the vibration through the car, to prevent this, I'm giving it a couple of hundred extra revs when stationary which seems to smooth it out. When driving, the power delivery is smooth and there are no noticeable "jumps" when i put my foot down, it just seems like I'm a bit down on power and the car isn't ticking over properly at idle.
If I have the engine running and the bonnet open, I can hear a ticking noise coming from within the engine bay, (I'll take a video of it and post it a bit later on, If anyone could anyone tell me if this is normal noise it'd be appreciated)
So far I've done the following to get to try and solve the problem:
Replaced all 4 original coil packs, I've also tried swapping coil packs over but the fault doesn't move cylinders so I replaced cylinder 1's again but this didn't solve the problem, also the coil pack doesn't seem to be popping up which could cause it to "miss" the spark plug. so I'm pretty sure the coil pack isn't at fault.
Replaced the spark plugs twice - The original plugs were replaced with OEM ones at a service some 3 months back, the problem continued so I took the car back and the garage replaced the OEM plugs with heat range colder ones to in case the plugs were overheating causing the coil pack to fail.
They also did a compression test - no problems found
I've also put some injector cleaner into the fuel tank just in case it was a sticking injector causing the problem, and I cleaned the MAF sensor as per wak-tt's guide but it's not solved the problem
So - what's next to check, i was thinking it could be an electrical problem, perhaps a damaged wire somewhere in the loom but i can't seem to work out how to get the silver heat shield off without damaging it - does anyone know?
or - perhaps a fuel pump problem - But i would have thought if this was knackered it's cause all the cylinders to misfire not just one
If anyone has had similar problem or could point me in the direction of what to check next it'd be very appreciated.