First thing to check for a "jerky" cruise control is the speedometer cable. Does your speedometer needle vibrate or fluctuate? If it does, this is likely the cause of the jerky cruise control. The speedometer cable is a relatively easy replacement.

Just make sure you buy an OE quality one, for our 86 190e I replaced the speedo cable and got a no-name brand one and it had cheap connections and shotty quality.

__________________
Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE