Hey Scratchpaddy, help me understand what you're saying here as it doesn't make sense to me.

Quote Originally Posted by Scratchpaddy View Post
...when you lift off the gas to change gears and the throttle plate immediately slams closed, it causes a sudden increase in crankcase pressure, pushing more oil vapors through the PCV system to be burned off in the cylinders.
I always thought that closing the throttle could cause a spike in manifold vacuum, controlled only by the amount which the throttle is controlled/restricted by either the ECU or an idle limiting screw. This temporary vacuum condition would help draw in crankcase blow-by pressure and in turn reduce it.

Quote Originally Posted by Scratchpaddy View Post
The air/fuel mixture also leans out momentarily, causing a spike in NOx emissions.
Same here. With the throttle closing, it not only restricts air but inherently causes a temporary rich condition, until the emissions controls kicks in. That might be the single biggest benefit to having a control-by-wire throttle, is the ECU can better manage the air-fuel ratio and in turn what gets sent to the catalytic converter.

I got this from studying emissions controls from 1970s era systems growing up.