When the last time you check the engine oil? Could be it. Low oil pressure will do that if its not reaching all the way up and not being lubricated properly. Or your oil is too old and looses its vicosity in other words its too thin. BTDT
Get a garden hose and use it as a doc's ear and listen to it.-Could be lifters/lash adjustment or some other worn out parts in the valvetrain.
Monday, August 13th, 2007 AT 6:34 AM