Find the line to the transmission. On the '85, it's probably coming from the blue flying saucer on the driver's fenderwell. Or, it could be coming from the VCV directly if it's an older build.

Get a vacuum gauge and T into this line. Route the vacuum gauge into the cabin and take it for a test drive. Observe the vaccum levels at various pedal positions........idle........1/4 pedal........1/2 pedal.........3/4 pedal........and full pedal.

Report back with results.