This is similar to, but not the same as my question Effects of Dirty Piston Heads and Intake Valves.
Basically, I often see people talking about taking the intake manifolds off older cars to clean them, or to seafoam them, separate from just trying to get the valves clean.
However, I would think that unless there is a major problem with the engine which has caused a truely massive buildup of gunk then a typically dirty intake manifold shouldn't really be much of an issue.
The only things I could think of would be that maybe a dirty intake could throw off ECU fuel calculations relating to the assumed Tau pool on the intake walls, but that would seem to be a pretty small effect I would think.
The other thing I could think of might be clogged EGR passages, but I don't think seafoaming would help with that.
Anyways, what are the effects of a typically dirty intake manifold?