When the cruise control is on the car feels like it's surging. No indicated change in speed. I wouldn't call the symtom "hunting" there is no ON and OFF sensation or indicated change in speed.
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2001 Volvo S60 Question: surges and hunts in Cruise Control
Answer #1Bret Bodas from RepairPal Test Shop, December 11, 2009, 09:53Master
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.