Maybe you are getting dirt, rust or something else
in the fuel lines to the injectors and that is hanging the injector open. New fuel filter? Blow out the manifold line, check fuel pressure.
I remember about the tightening of the manifold now. I think it was Beav that recommeded that. I was the one talking about all the bolts involved.
It could be intermittent as the metal is warming up to operating temperature. Diffferent expansion rates between the manifold and heads. If you found some the bolts loose, the gasket could be shot.