V6 TDI 272, engine light on dash / missfire when cold?

[Ian A4 Allroad V6]

Hi,

I bought a 2017,  76k A4 Allroad a few weeks ago.

Took it to Audi for an inspection service.

After collecting, 5 minutes in to my journey home, the yellow engine light came on permanently.

I took it straight back, they plugged their diagnostic in to it, only to find that the only real problem was the foot part of the throttle, which to me works absolutely perfectly. But they wanted £212.00 +vat per hour to investigate!!!!

They also noticed a missfire, very occasionally on cold start up.

Ive taken the car back to the garage I bought it from, who have put their VAG kit on it, only to find a dodgy volume switch, and the pre-scence is sporadically iffy. 

Nothing aligning with Audi at all.

Strangely, the engine light went off as I approached the garage, that was after 2 hours on the motorway.

So no light shed from anyone as to why the l engine light actually went on?

The car garage have now taken the car to a specialist to see what the missfire is about?

Any thoughts gratefully received.