Hi. Not sure if this is the same setup but i had a Z16XEP astra with the same dtc that had me going for some time.
Has this got a split inlet manifold?
The one i did had bad carbon build up in the EGR gallery within the manifold not letting egr gas's through and effecting fueling, small egr tracks into each port where badly blocked but not enough to stop smoke on the smoke test.
worth a look.
cheers
john