Cruise control issues...

Hey all,

A friend just purchased a 1991 Accord EX as her first college car. I am attempting to diagnose a cruise control problem. Initially it didn't work at all. I found that the vacuum tube going to the cruise control module/diaphram was disconnected. After connecting it I experience the following:

- Travel 50 MPH on flat, straight road
- enable cruise control (button on dash)
- press the "set" button on steering wheel and immediately release gas pedal

The car then slows to about 42 MPH then the cruise kicks in and slowly increases speed to 50 MPH-ish. Pressing the "accel" button on steering wheel increases speed.

Is this normal or should it respond faster? I suspect low vacuum. I hooked up a vacuum gauge at idle and it reads just under 15 psi at idle. I'm not sure what normal should be. After car is shut off, vacuum drops fairly rapidly (within 3-4 seconds) to zero. Should it hold vacuum for a longer period of time?

Could it also be a sticking cable? I exercised the mechanism under dash and it seemed to move freely.

Any help is greatly appreciated!