Mode delivery problems on those cars was always due to a vacuum problem.
It could be the vacuum supply system or an actuator vacuum motor problem.
Is that the big rear wheel drive car or the smaller front drive car of the mid 80's? I forget now.
At any rate, if you can get the control head out you can check the vacuum connection at the control head for supply vacuum.
I made a little tool that let me run vacuum to each "motor" individually and check them for leaks.
The vacuum switches used to break a lot too on the control, they can be serviceable if you can find the parts.
It could be the vacuum supply system or an actuator vacuum motor problem.
Is that the big rear wheel drive car or the smaller front drive car of the mid 80's? I forget now.
At any rate, if you can get the control head out you can check the vacuum connection at the control head for supply vacuum.
I made a little tool that let me run vacuum to each "motor" individually and check them for leaks.
The vacuum switches used to break a lot too on the control, they can be serviceable if you can find the parts.