Some other points on this topic, as I've recently had to deal with pcv and such issues.
Take a little step back for a moment: look at the 2 main parts of the air intake system: the inlet [filter end] and the intake manifold itself.
- You have air coming in from your filter, and eventually all of it gets into the intake manifold.
- The MAF sensor measures the total amount of air coming in from the air filter; all that air somehow finds it way into the intake manifold, some of it via the throttle body, some of it through the pcv. As long as all the air entering the intake manifold is measured by the maf, it's not important where the air is coming from. [ignoring intake air temps for this dicussion.]
- At the intake, it will pull air from wherever it gets it from paths of least resistance and per air vacuum/pressure dynamics. An open throttle body allows more air at less airflow resistance, while the pcv allows some air flow but in a restricted manner.
The amount of vacuum produced through the intake manifold is proportional to how hard it has to 'pull' or suck to get air into the engine.
With a closed throttle body, the vacuum will be at its highest, and that's when the greatest pull (suction) occurs on vacuum lines, incuding through the pcv valve and hoses. At this stage, some air will flow through the thorttle body, and some through the hoses into and through the crankcase; all going into the intake manifold.
As engine speed increases, the vacuum produced by the intake manifold drops, as the opening of the throttle blade makes it easier to get air in. More air is then flowing through the throttle body, less through the pcv.
At WOT, the throttle is wide open of course. Vacuum is at its least here, or not present at all. The PCV closes and no air gets pulled through its vacuum and all air comes through the throttle body.
But, for all three scenarios, ALL the air going into the intake manifold has been measured by the MAF sensor, so the computer knows what air should be there.
Now, if youy have a vacuum leak, even a very small one, it will affect the amount of air entering the engine vs. what the maf has measured. Some experimenting I did with my V6, even with like a 1/8 vacuum hose, it affected the air/fuel trim adjustments made by the computer by about 10% at idle; there was enough unmetered air coming in (and not measured by the maf) to throw off the actual air used, and as the closed-loop O2 sensor systems are designed, the computer compensated for the exrta ait by adding 10% more fuel, at idle.
Besides all the above, when you have forced induction, it can become tricky and even more important to make sure that all the air is metered. The location of the MAF is then very important when it comes to breather hoses, etc., to make sure all air gets measured. (This was a real challenge in my supercharged blow-through setup, BTW.)
And with boost, you also have to be more aware of crankcase pressure that will arise when under WOT, and how that pressure is vented/releived. THe PCV 'should' be closed under boost, and so that port on the valve cover should not allow any air to go in nor out of the engine. Typically, the breather hose from the air intake provided the releif for pressure under WOT.
Hope this helps.
It feels like the throttle body is short circuited.
For example, if you made all the hoses 5/8" diameter, the throttle would now need to be almost closed, since almost all the air is coming in through the PCV lines. It may have more difficulty controlling that small amount of air. I haven't seen anything in the tune that addresses this issue directly. There are a couple tables though that map out load vs. throttle position, and airflow vs. RPM...
