The engine is detonating at medium throttle in any gear or speed?

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