2003 Sable V-6. 24 Valve Problems
 

We have a 2003 Sable with engine problems. The engine misfires under load and the engine light is on. It gives a PO316 code and also identifies cylinders #3 and #5 as misfiring. It got new plugs 20K ago and had the front valve cover gasket replaced because #5 plug well was filling with oil and fouling out. Any advise???