1985 Chevy Silverado loss off oil pressure when idling

Engine Mechanical problem
1985 Chevy Silverado V8 Four Wheel Drive Automatic 11000. Miles

Hello: I am having loss off oil pressure when stoped at a idle, for about 10 seconds. I have changed the sending unit. No change. I also have a knock or tick not sure which that goes away as I build rpm's. Im a bit off a back yard mechanic, but have never had to deal with this. The motor is about a year old GoodWrench new not rebuilt. I started my truck tonight in the dark and noticed a bit off blue light(fuel burning I presume). It was on the drivers side at the head. I have had problems keeping my headers tight, and been told that I may have burnt a valve as it has been letting in cold air. Any help, advice will be appreciated. Thank You;
unomenotbutmight@yahoo. Com Wayne Marchington