Volvo Repair: 1987 760 TURBO 2.3, control circuitry, vacuum control

Question
I STARTED MY CAR AND IT STARTED REVVING HIGH RIGHT OFF THE BACK, SO I SHUT IT DOWN.  I HAD A FRIEND LOOK TO SEE WHAT WAS HAPPENING AND THE CRUISE CONTROL DIAPHRAGM WAS BEING DRAWN DOWN.  I ENDED UP DISCONNECTING THE VACAUM HOSE FROM THE T CONNECTION GOING THRU THE FIREWALL TO THE SWITCH I GUESS.  HAVE YOU GOT ANY IDEAS WHAT MAY BE WRONG?  I DO NOT WANT TO DRIVE WITH THE VACAUM HOSE OFF FOR TOO LONG.. J.

Answer
could be a few things:

1) failing cruise engagment - being activated all the time
2) failing vacuum control valve - no matter what the cruise control is trying to do the control valve is sticking open
3) bad vacuum check valve - going along with number 2

hard to list a whole trouble shooting procedure but if you have access to a service manual of some kind than you'll have a visual reference to double check components that are suspected faulty.  vacuum problems are easy to find because you can pinch off hoses and easily isolate the area.  The only electronic part you have to worry about is the control circuits.  Double check all the vacuum stuff first and if everything there is working like its supposed to than start troubleshooting the cruise control circuitry.

James