if it was a big end bearing, wouldnt u still hear the tapping when ur off the accelerator (ie decelerating) ?
i would have thought there would be a constant tapping, either accelerating or decelerating?
when u start it cold, have a light sniff around the exhaust manifold/turbo area, if it smells of fuel, i think its the exhaust manifold gasket.
for me it explains most things, but doesnt explain the idle.