In a 1989 Chevy van with a throttle body, the vacuum line from the transmission likely runs to the
Transmission Vacuum Modulator Valve (TV Cable/Vacuum Modulator). This valve is located on the transmission itself, and controls shift points and firmness based on engine vacuum. It's crucial for proper transmission operation.
It's *less likely* to go directly to the intake manifold or throttle body itself, though some vacuum may be *sourced* from there for the system as a whole. The modulator is the final destination for the transmission's vacuum line.
