I too was concerned about a possible valve adjustment on my '84 245 because of a twitch in the idle, after I called a small garage near me that specializes only in volvo this is what he said, "volvo leaves enough clearance in the valves that a valve adjustment only needs to be done about once during an average life of a volvo." He also said that with my car at 216K it has already probably been done.

Before you rush into a valve adjustment, I would try the easy fixes like meticulous tune ups as Jorn suggested and then if it still is idling funny take it to someone who specializes in Volvo's (there are plenty out there who are not dealerships, cheaper too) to see what they say. Most will have you pay $25-50 to look at it, but that the $ is good towards service on that vehicle in the future.

Good luck
Chuck
'84 245 216K
'88 244 154K
'85 744 174K