1996 Volvo 960 from North America - Comments

Rough idle 6 cyl. 2.5 '96 960. Replaced the blown inlet manifold gasket and now it hunts at idle when cold only, and has no power past half throttle. Vacuum gauge reads "late valve timing", but everything is controlled by the ECU so don't know what to do next. Battery went dead flat while working on it if that helps? May be it just needs a relearn or something???