1996 Oldsmobile Cutlass mileage: 115,000. My car has detonation problem at medium throttle in any gear or speed. Timing chain was replaced 15,000 miles ago. I have checked belts, vacuum lines, EGR valve, vacuum to the EGR valve and timing, which is twenty degrees BTDC. I have noticed that while checking timing mark, timing will not advance while snapping throttle. Is this a computer problem or other component problem? Thanks, John