I have a '96 Caprice Classic with a 4.3L engine. After having my car serviced I noticed a month later I seem to be missing a vacuum line with a blue elbow that inserts on the intake snorkel. I think it's the opti vent line. Anyway, lately the car has stalled at low speed but restarted again.
It also surges or bucks at lower speeds around 30-40mph. No check engine light, yet.
Does anyone know what the vacuum line mentioned above does?
Could it be the source of my problem?

 

The vacuum line attaches to the top of the intake throttle body inlet (rubber 90 deg. elbow) the intake air draws/sucks the moisture out of the dist. you want to have that connected (important) as the moisture (condensation) will ruin the dist. opti-spark unit.
It is a expensive unit to replace.
CC