Should not have caused a problem with the idle - unless the plug reach, plug gap, and plug temp range are off. I'd make sure that the coil on plug modules are on tight - might have to look at the boot end and see if there is any corrosion in there. Dielectric grease might help (basically silicone grease - helps keep moisture out of there to prevent corrosion.
Did you add any anti-seize compound to the plug threads? Used to be common fair with some older engines - but I've seen many newer engines being very sensitve to the coumpound. The plug reach is far enough that any extra anti-seize compund that gets worked in there will cause engien misfires and detonation.
Let us know what the turn out was.