Turn out my BBK 52MM "CA Exempt" throttle body's port vacuum nipple is non-functional thanks to their design and gasket. Their older TB's had the port vacuum, like the stock TB's. I was able to notch the gasket up to the bore and reassembled so now that nipple has manifold vacuum. I also verified driving around with a vacuum gauge on the valve that my EGR system is functioning as it should be when I drive.

The only thing I can think of is that port vacuum MAYBE allows a smoother introduction of vacuum once the EGR solenoid opens but even then the valve diaphragm is large so I don't see this making a big difference.

OR, it's a failsafe if the EGR solenoid fails, stuck open, the EGR won't be open at idle.

Welcoming any ponderings.

 

Depending on the year, the timed port can also serve the EVAP purge solenoid valve. I believe you are correct, that this is a redundancy in case the solenoid control system fails in some manner. You are also correct that it probably make little difference, specifically for the EGR since it is likely a negative backpressure valve, and that would probably create a more significant idle problem if the solenoid fails.

 

Thanks. So the car did finally pass CA emissions using the manifold vacuum, but I still replaced the BBK TB with a factory unit and car runs like new. Also, I think you are correct. I believe the evap cannister purge solenoid taps off of that port vacuum as well.

 

I've had issues passing smog for years because of my EGR solenoid. So before I head to the smog station I disconnect the vacuum line from the bottom of the TB and from the EGR valve and plug the lines before I tuck them in under the manifold. Then I run a vacuum hose from the TB under the plenum and connect it directly to the EGR valve. It idles a little rough, but it passes every time when I do this.

I may be wrong, but I am pretty sure that the evap cannister does not use the vacuum from the port under the TB. I believe it uses one of the vacuum ports/hoses from the passenger side of the TB.