Cobra123089
Member
This is actually a pretty sizeable vacuum leak.
In the OE setup, the source of air for the driver's side VC comes from the intake duct, after the MAF. As you note, air enters the driver's side VC, passes through the crankcase and is pulled into the plenum. Again, in the OE setup, this air is accounted for by the MAF. In your setup though, the air is being pulled from under the hood and the MAF doesn't know about it. This isn't the equivalent of a small pinhole or crack in a vacuum line: All the PCV hoses are fairly sizable.
You probably won't notice it at idle since the PCV valve is basically closed then. If the valve did stick, you'd probably have a crazy idle since you'd be getting unmetered air bypassing the IAC valve and throttle body. At part-throttle cruise, when the PCV is open, the PCM is probably just compensating with fuel trims when in closed loop. It would be interesting to see the ST and LTFTs out of curiosity.
At WOT, it is technically a vacuum leak but the volume of air entering the engine past the wide-open throttle body probably swamps whatever the PCV is contributing. As well, since you're feeding to the plenum, at WOT there's not a lot of vacuum there anyway so the amount of unmetered air is fairly small.
So it's really at part-throttle that this becomes a concern. If the leak isn't too bad the PCM will just adjust for it. Still... it is a vacuum leak
I dont see how its a vacuum leak. The air never enters the combustion chamber therefore it can not affect a/f ratios. I understand that the stock PCV vents after the maf in the intake tube, but that air/oil should not have o2 in it. maybe you can explain better.