Cruise Control Freakin' Out
 

This morning in a heavy rain doing 60 down the highway with the cruise on, the car started surging like every half-second. I cancelled cruise control and it stopped. I re-engaged it and it did it again. It keeps doing this accelerate-decelerate over and over every half-second. What's doing this?
Pomp

Mine is doing the same thing. Do a search under "cruise control amplifier" or "cruise control amp." - will give you lots of info.
BTW - I found out the hard way about using the cruise in heavy rain - totalled a brand new (three month old) S600 sedan because I hydroplaned. Needless to say the insurance company dropped my parents because of that one. I was very lucky to have walked away from it with only minor cuts, bruises, and a couple of broken ribs.

I just drove it. It's not raining anymore and the cruise is working fine. Do your symptons come and go? Or does it consistently work wierdly?

At first it came and went - now it is pretty much constant. I need to replace mine altogether (cruise amp.).

What was the temp. there yesterday? It could have an effect on the amp.