The 1999 came with ETM issues, the factory extended warranty to 10yrs or 200K miles. Dealers have been known to first reprogram the ETM before replacing it with better units.
Variable Valve timing, very nice until you change the timing belt. Requires that the engine be turned 90 degrees past TDC and then back to TDC before removing belt.
Coil overs. #3 tends to fail first giving a code for misfire. The heat is what kills them. At $40/coil replace only those that fail.
The cabin filter must be replaced to keep the evaporator clean, otherwise the evap will spring a leak. Replacing the evap is like replacing the cabin heater on a 140/240, it hurts.
All the rest is straight forward mechanical maint.

If the Tbelt hasn't been changed, most 1999s got changed well before 100K, change the tensioner also.

Klaus
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Volvoless. Sold the R. There is now a void...