base model 1998 S70 with 61k. Every now and again, while sitting at a traffic light or stop sign, the engine will "hiccup", with idle dropping 3-400 rpm, and then idling normally again. No codes set, and the dealer was less than useless. Sign of a fuel pump going south?

I would suspect fuel filter before pump. These pumps are pretty sturdy. The fuel pump relay (103) has been improved and should not fail. The idle control valve may be sticking, you car doesn't get much use, and can be cleaned with carb cleaner.

Klaus
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1975 164 w/174,800mi (Sold) 1995 850T w/91,000mi, 1998 V70R w/129,000mi

My 960 is doing the same with black smoke from the tail pipe at the time of the hiccup, I order the oxygen sensors. Take a look at the tail pipe to see the inside is black.
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1996 964 160K, 2000 S70 60K