White plugs mean its running too hot. High NOx. Lean condition. I bet your CO is low -- around 0.10 or lower, too. Replace the plugs to spec and clean the EGR passageway while you're at it. After you clean the gunk out, apply vacuum with a hand pump to the EGR at idle. The engine should stumble if the EGR is working. If not, it's either still clogged somewhere or the diaphragm is broken.