I drove my 1993 Ram over 300 miles to visit family this Thanksgiving Holiday. During my trip, I decided to flip on the cruise control and sit back and relax. When I set the cruise control at 65mph, the engine tried to maintain the speed but the engine kept reving up and down (100-200 rpm difference). This got really annoying hearing the engine surging up and down, up and down......on and on. I turned off the cruise and went most of the way without. What could be causing this condition? I have used the cruise control several months ago with no issues.

 

Crank position sensor? No other symptoms?

 

Turned it up some more since the last time you used the cruise?

 

The only thing I have done different since the last time I used it is installing a performance fuel pin.

 

Still trying to figure out whats causing my jumpy cruise control.

 

This will sound strange, but you need to check your driveshaft slip yolk.The yolk at the tranny. There is a bolt, don't remember what size, in the yolk. This bolt holds pressure on the speedometer gear. Said gear is captured between tailshaft bearing and the end of the yolk.
Trust me, if it is loose your cruise will do crazy things.
Had this happen to my truck. Took me forever to find-fix it.
Hope this helps.
GW