Oil Pooling in Intake Manifold

I think the reason oil is coming through is the PCV valve location, below the head, on the block. Gen 2 had it atop the valve cover.

A more efficient oil catch can, and/or a pair in series, would likely be more effective. Still not 100%, but to where you’re getting the bulk of it, and the intake manifold interior is just “oily”, not a swimming pool.

 

It is one of many gen3 issues which was corrected in later gens. Oil and water vapors can condense as well. Most people do nothing about it although quality catch cans and periodic intake cleanings are options. With the catch cans you have to be diligent to keep them flowing or you can easily blow the timing chain cover seal, still another flaw. Since most people can’t be trusted to even check oil levels, manufacturers do not include manually emptied catch cans. More recent Toyotas have a built in catch can that drains back to the engine.

 

There's more to a PCV valve than you think; it's a calibrated flow vs. vacuum device that's meant to closely match the engine's blowby production at different operating points, when installed in the designed orientation, which Toyota can be safely assumed to know. As a second job, in the event of backfire, it needs to close to keep fire out of the crankcase.

It was atop the valve cover (still horizontal) in gen 1 also, and as early as gen 1 there was already talk of the usual puddle in a Prius manifold. There was definitely a puddle in mine. The late intake valve timing was widely suspected to contribute. There was little talk of any ill effect.

 

Good point about a possible backfire. I would go directly into the catch can in my case. Something to think about.