At wits end with 1993 240 Cruise Control

[dmg4]

Somebody, please help me with this 1993 240 Cruise Control Kafuffle.

My cruise control is on the blink. Here are the symptoms. The vacuum actuator will only pull the accelerator pedal down about 1/4", even when coupled directly to the vacuum pump on the firewall, and I run the pump constantly by jumping the connections directly to the battery.

I have replaced the stalk on the steering column, the pump, the vacuum actuator and the ECU with new OEM parts, to no avail. I though it might be a vacuum leak somewhere, but why does it not pull the pedal to the floor when the pump is hooked directly to the actuator, thus bypassing all the hoses that might leak. The actuator is new. The pump is new. The ECU is new. The stalk and switches are new.

It gets better: if I hook up a more powerful vacuum pump, the actuator DOES floor the pedal.

I thought perhaps that the kickdown cable, which is a bit sticky, might offer too much resistance. Thus, maybe that little dinky Volvo pump is simply not strong enough, and that's why the more powerful pump can floor it. But I get the same outcome with the kickdown cable disconnected when using the Volvo pump (again, connected directy to the vacuum actuator) and the throttle pedal seems very light anyway.