3.8 Mommyvan off idle knocking...

I too had a 3.8 that developed a very light knock, only at idle at around 190,000 miles...Funny thing was, it seemed to start with the only non Mobil 1 oil change I ever did on it (Wal-Mart house brand full-syn, they were out of Mobil 1). I never got into to it to check it out... ran perfectly to 230,000...Then my daughter got hit head-on and totalled it. I had no qualms that it would have continued on for a long time to come, it never got any worse in those last 40,000, and at 230,000 I still didn't need to add any between changes.
So much for me being helpful...