Reasons I have found for idle adaptions failing - Faulty CTS (even if it tests ok) Faults in EMS Engine temp too low (on some systems) Faulty T/body (rare) I have had a few where I had to clear adaptions first. The only tool I know of that will do this is Vag Com.
I have seen 2 of these with faulty hall senders that did not log a code for CMP but the CMP was shorting the ref supply.