Inlet manifold gasket not being compressed enough, due to pulled bushing, warped manifold or elastomer just not sealing, Coolant weeps into cylinder and can cause rough running especially when cold.
Best solution is a late alloy VVC manifold, but look here. Describes the issue with a plastic manifold and what can be done to address.
https://the75andztclub.co.uk/forum/s...inlet+manifold