erratic cruise operation

[a12play12]

Hello,

I have an 83' 380SEC. the cruise controll will work if i run the vehicle on the lift, and for approximately 2 hours afterward. If it sits for more than 2 house there will be no cruise operations at all. I have inspected the relay for poor solder joints, bench tested the acuator (clutch and motor), and check switch functions. When the cruise operates all functions do work, however there is a rapid surging at all speeds worse at lower speeds (30 to 45). Thank you in advance for your assistance. R