I recently had a shop convert my car to a non-cc carb and vacuum advance distributor. Everything seems to run well now except that when I try to use my cruise control, the car just begins accelerating without seeming to want to let off.
Since I got the car back, I have noticed a variable hissing noise that seems to come from the dash. It varies in intensity to the throttle.
As I have checked the hoses in the engine compartment and changed the bad ones out, what is there near the dash/firewall that might have sprung a leak? I am leaning toward the possibility of the vacuum control for the environment control.
Will a vacuum leak cause the cruise to accelerate trying to match vacuum? I don't quite understand how cruise works anyway and can't seem to find info that explains it. BTW, I have a mechanical cruise.
Thanks for any input!

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1983 T/A, stock 305, Edelbrock 1904 carb