EVery so often, I hear a noticable ticking at idle on my 98 960 w/93K. In going over the service records, I see the PO had the Volvo dealer treat this problem before. The Volvo dealer used Marvel Mystery Oil to treat it. It goes away quickly enough without any additives but you can sure hear it when it's there.
Sounds like....well, it sounds like a valve tap!

What is the science behind a sticking valve? What is the tried and true remedy?
I use dino with a 3-5K change interval, Mann filter.
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93 945 109K , 94 940 106K ,98 V90 89K

Deposits form on the valves when the hot valves come in contact with gasoline and engine oil. Over time, these deposits can build up and cause the valve to not move as freely as it would if they weren't there. Hence the term 'sticky' valve.

As Poolman suggests, a clean engine (Auto-Rx), synthetic engine oil and the occasional high rpm run keeps the valve deposits down.

DEWFPO
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1998 S90 071,245 and 1995 964 154,100

What about an Italian tune up?

"occasional high rpm run" in my previous note.

DEWFPO
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1998 S90 071,245 and 1995 964 154,100

I have had the same problem but it's been quiet some time ago, other than when I knocked the oil cooler off of mine and ran it out of oil last week,they really tapped after I got everything back together,alls fine now though.
Okay go to www.AUTO R-X .com buy a couple of bottles of their mistery stuff and follow the application procedures and afterwards change the oil out to synthetic,personally like Mobile 1 in mine, also flushed the tranny as described in the Faqs and switched to mobile 1 there also, these cars love the stuff, I'm running 0-40 syn in the engine and will go a little heavier when warm weather gets here.
Follow the above and that should take care of your problems,
Hope this helps
Poolman