Lower than 100kpa at WOT could be elevation too, if this log happen to be somewhere higher than your used to logging take that into consideration aswell. Id think where you have the filter should be a good spot for air. unless the aero is really creating a negative pressure spot for some reason. If thats not the case id think your on the right track with looking at valve train stuff. But don't rule out the sensor itself or the hose feeding it.