2006 Audi A6 3.2 Liter Runs Rough and pops, misses for 30 to 45 seconds, only with cold start up

Originally vehicle had a CEL on, found a broken plastic vacuum line to the intake manifold by cylinder head on bank two. There was a related TSB to the issue. Replaced broken line and cleared faults, set readiness car ran fine. Two weeks later customer returns with a rough running, missing/popping issue only at cold start up for about 30-45 seconds, won't take throttle properly. Than car runs fine, does not miss re-starts fine. I have replaced the spark plugs, the low pressure fuel switch, removed the upper intake manifold checked for other broken vac. lines were o.k., checked operation of manifold flap diaphragms(o.k.) cleaned intake valves of carbon, cleaned the throttle body, performed a capacity discharge on the battery, ran throttle adaption and fuel pressure adaption. Car shows evidence of running rich old plugs were black with soot. Don't think it is a lifter issue(not pumping up) as per TSB. Issue remains, I use the VCDS scan tool by Ross-Tech for my info. Any ideas would be greatly appreciated. Thanks, Chris