surges and hunts in Cruise Control

Hello, The 2001 S60 had some issues with the electronic throttle, so much so that they extended the warranty of the throttle module to 10 years and 200,000 miles. The throttle module is likely the issue here, it may need to be cleaned, have the software updated or even have the module replaced. Besides the throttle module, you may have an issue with a vacuum leak or the MAF sensor, but I suggest you take it to the Dealer, see if the throttle module is the issue, so they can address it.