[V8] mixture adaptation/idle issue

[John Dodd]

As a follow up to the ongoing saga that started almost 2 months ago here
is the latest:
I went to the dealer to have the codes read even though I did it
myself.Here is the readout:
 
00561 Mixture adaptation 
Adaptation limit( add.) exceeded
 
The idle on the car goes down to 300 -400 rpm in drive then back up
again to normal..Power seems Ok but not as before.It even idled Ok for
awhile .(intermittent issue ?)
Any suggestions ?