You might want to do a engine running valve adjustment. Start by backing each one off one at a time till it clatters real good. You will know when you are there. Once you are satified its loose and has clearance, slowly tighten it back down till it quits clattering. Then go 1/2 turn more. Do this on all 16 and see if the noise goes away and it idles better. It helps to slow the idle way down before starting this and pull one rocker cover at a time to keep the oil mess down. Joe