[texasprd]

I've got an '88 1500 Silverado w/ 350 and TBI (w/ MAP sensor port at back of TBI unit). It appears that the vacuum port for the MAP sensor is plugged - I have 0" vacuum on vacuum gage w/ engine idling or above idle, good 5V reference to sensor, 5V coming out which drops to 0V when I remove harness connector, voltage varies as expected when I apply vacuum w/ hand pump. I seem to have inflicted this on myself yesterday when I pulled the TBI off to do some maintenance, and decided to make sure the MAP sensor vacuum port was clear - if there was any crud in there, I must have compacted it. From the back of the throttle body, it apparently goes forward internally - my question is: where in the TBI does the MAP sensor port originate? I know the PCV/evap/EGR ports originate at the front of the unit beneath the butterflies. Where does the MAP sensor port originate and actually get exposed to vacuum?

Thanks for your help!!