Bad Timing Chain or Camshaft Position Sensor??

[GJB]

Any help/opinion would be great. 2007 Audi Q7 4.2 80k miles. bit of a read but worth it for the dealer experience. Always ran great. Suddenly while wife was driving started running rough, misfiring shaking. Started it a couple times, same issues. i ran reader on it and OBD codes p00016 (and another couple iirc 0340 was in there and a specific cylinder number misfire code). Dont know a lot about these engines. Figured maybe a bad coil or sensor hopefully. Towed to dealer, dealer does an assessment tells me the timing chain skipped, needs new timing chain/accessories plus a complete rebuild at a cost of $20k the engine is shot. confirmed with them they checked it out and its not a coil or sensor which they assure me they did. Love this car but cars not worth that much, and i know the chains are at the back so wont be cheap at smaller garage either, so dealer offers me 1200$ for the car. So i decide to cut my losses. I go to the dealer sign it over and go clear out my personals from the car. Decided to try and start it , and BANG. Starts fine, runs perfectly, took it for a 20mile trip around area to be sure, no issues. Of course im pissed, call out the general manager of the dealer who was surprised of course. The garage was closed this time but calls the head mechanic on the phone at home and then tells me he spoke with the head mechanic and he said the timing chain must have jumped back to the proper timing. like i said i dont know a lot about this engine but most engines just dont jump back a tooth to correct timing position. So Im still pissed at this point they confirmed to me the engine was shot from interference and my car was basically scrap and were going to steal it off me for 1200 bux and make a good chunk of change at auction for it. I doubt they even really checked it out, just hoped id buy a new one right away, or they would make some cash at auction (which i found out later this dealer own his own auciton) Absolute terrible borderline crooked dealer experience aside Im happy the cars not shot!

Anyways sorry for the dealer rant, but my question is anyone have camshaft position sensor issues with the 4.2 that caused pretty good misfiring/shaking? or maybe another issue im not thinking of? Any input would be great. thanks guys.