Hi Dave,

I got your pictures in my emails so it’s not junk mail either.
I’m glad I figured out that what’s in your profile is only shown to yourself on some of those blocks.
It just didn’t click in my ole’ noggin.

I hope that the newer vacuum controller is the problem too.
It’s not suppose to pass vacuum below, to the vacuum motor, until it’s turned on and above 35 mph.
I have never had one of those apart, so your glimpse inside one, has probably not been documented by anyone. Maybe even Art Benstein, an automotive necropsy expert! (:-)

Your picture shows a honking big vacuum can or reservoir, for just a cruise control unit.
If a engine is under a heavy load, the vacuum drops “enough” that the cruise control quits.
The large can delays that reaction.
Looks like it is fed from a vacuum source that is for the cabin controls.
That feed has a restricted port fitting screwed into the intake manifold.
That line should have a two colored check valve and it looks like it does.
Why they want it sealed it off like for use like the cabin controls is beyond me, but maybe it’s not?
Something might be weird or normal around here?

We need to get this system sorted out and get the setup as close to a factory installation link I found.
Like I said, a vacuum can is questionable for being there as a little electric vacuum pump is used on these cars mounted on the drivers side firewall.
It gets turned on, probably with the signal stalk switch or the black box controller, after the stalk switch is used by the driver.
Constant vacuum isn’t needed and safer if its not there all the time. IMO.
As it is now, if that cruise system leaks anywhere it will be behind the AMM of which effects mixtures to a determinant slightly.
Emissions on later cars probably tightened that up, especially on the 90’s and up.
Do you have an extra wiring connector (a later version) to run a vacuum pump coming from up under the dash controller someplace and to go outside? I don’t think you have and we don’t know if the controller under there is a 1986 with 1989+ pedals. Volvo changed things around a lot. A mixed bag!
If not, someone placed the can out there instead.
That why I say it can operate on a very limited vacuum source as the components are small like the cabin controls are.

Enjoy your weekend!

Phil