Revs replied:

Wal, I assume the Rosta CC is an "after market" unit? I am only guessing, but I suspect that you may have a problem where the vacuum line that sucks the piston back , operating the CC., is not being shut off electrically. ie: the suction is maintained on the piston of the CC unit even though the dump valve is fully open. There are two valves in the operating unit, one to open the vacuum line (effectivelly pulling the piston back, speeding up the car), and another valve to "dump" the vacuum, (which works in tandem with the other valve, ie: opens when the other closes, to slow down the car) I suggest you check the continuity of both these valve with a multi meter. This MAY identify the problem. Good luck.