Low oil pressure at idle.Try a different oil,say 20-50 valvoline racing oil.Probably gain you 10 psi at idle.I was told by a Jag mech. to run nothing but 20-50 in my v12 xjs. I run straight 50 racing in my mustang and on the hottest day it maintains 45psi at an idle.worth a try.Also at 60 miles an hour if your oil light comes on the damage is already done. Bryan