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Car not running smoothly. Idle is a bit rough. No warning lights. Audi roadside assist came out and can see the misfire being logged, around 50 in 2 mins, however, this isn't logging a fault code.

Guy was really helpful and tried a new coil pack and spark plug. Issue still there. Booked to go into Audi tomorrow for further checks. Perhaps it's a clogged injector. Any suggestions what else it might be?

if it's not spark related and the next step after checking the injector is working would be to do a compression test. Hopefully that won't be the problem though.

Cheers pal, hope it's something straight forward like the injector...

I know this won't put your mind at rest, but I'm friends with an Audi master tech who recently made a coffee table out of a 3.0T block. This is why:

The engine had a coolant leak from the internal supercharger cooler cores (they sit inside the body of the charger) and then what happens is the coolant effectively washes the bore of lubrication causing excess wear and loss of compression. I would say nothing to do with tuning however that's Audi's get out as it can't be proven otherwise. It's not common, I've only seen it twice.

A compression test will tell you more. But on the bright side, if the cause of your misfire is indeed this then you may have caught it early enough to have not done any major damage to the rest of the engine.

Shucks, I won't be able to sleep now.

Not great news...

Issue isolated to compression loss where a valve was not seating correctly. Dealership have agreed to replace head, valves, cam across an entire bank. Parts on special order from Germany.

Told it will take 5 working days for the bits to arrive and then a further day to complete the task. Is there anything I should look out for or ask?

Went to see the car and damaged valve. Surprised by the nature of the damage. One of the inlet valves had its edges burnt all the way round.

The technician appears to be taking a great deal of care in getting the job done right. Just got to sit tight and drive around in a Q5 for a bit...

Glad they're getting it sorted for ya, sucks about the Q5 lol

Car still not ready...they have ordered a tensioner...Any ideas what that is for?

Timing Chain Tensioner I suspect, if that was faulty the timing chain would have too much slack in it and could cause issues

Surprised by the nature of the damage. One of the inlet valves had its edges burnt all the way round.

Whilst any diagnosis over the internet is pure guess work, I suspect carbon build-up has lead to a valve not seating and allowing combustion gas past (and thus burning out- which is rare for an inlet).

My question to the dealership would be, if this is the cause, presumably the other bank is of a similar condition- what are they doing about preventing this?

Out of interest, what fuel and driving do you use/do?

I do a 40 mile commute pretty much each day...that includes motorways. Always use super unleaded 99 RON or above.

When I examined the open engine it all looked clean, certainly wasn't any carbon/black soot I could see around the head or valves.

How can I get the dealership to clean/check out the other bank anyways?

Did they give a reason for failure? Valvetrain okay? Was the valve damaged (other than being burnt)?

If you ask the dealership to determine the root cause, I'd be interested to know the results

Like you mentioned I did ask for an explanation for the root cause. No details have been given. I get the impression the dealership don't know for sure or are not prepared to share the dirty details.

In any case the entire head, cam shafts, valves, springs are being replaced.

The repair saga continues...Audi need the car for another week to complete the repair work. Timing chain tensioners on back order...