Gents,in my experience(this bit of info is from an "expert volvo tech")the vehicles from 99 and newer have special software that requires a download if any one of the many sensors is disturbed.My brother has 99 V70 T5 and it had the same problem with the idle "hunting" while at a light.We instructed him to clean the throttle body only!This was kind of difficult because the fan assy should be removed so you can get to the t.b.Usually over time it gets a lot of buildup that causes the electronic throttle to "hunt for a happy medium".The 98 and older are a piece of cake,just remember to replace the gasket.So if for any reason any of the sensors are replaced or tampered with by a shop that does not have the volvo software,beware that you car may not start and may trigger several codes.Hope this helps.