Hiya John,

Rev dips, could be dirty or failing electronic throttle module or the aforementioned pedal.

Alarm system - There's an old battery in the alarm module deep inside the fender of your car. The battery has leaked all over the rest of the electric bits. I was able to ignore it in my V70. but YMMV.

ABS service - can you get the codes read out? Could be faulty control module, could be a wheel sensor, or?

At 278K miles that O2 sensor doesn't owe you or anyone anything. Replace it. Cat. converters are robust and unlikely to be the problem all on their own.

Battery drain - How old is the battery? Sometimes they just give up, especially if a car is driven infrequently and only in the city. After about five years you're on borrowed time.

For all of the above, a site search and/or Google is your friend. You'll have to sift through the info, but you'll get better advice than what you get from me. ;-)

What to check on at 278K? My '01 V70 2.4T had a head gasket failure at 267K (and 5 years ago). So maybe a coolant flush if you haven't done one. Besides that my V70 was pretty good. Voltage regulator went out, but alternator brushes were still good at 200k+. Worth a once over around the car at grounding points and all the electrical connections at the battery, including the 12V accessory connections. These cars don't like poor electrical connections; they can cause all sorts of weird things.
The heater core connections tend to fail and leak (the rubber o-rings) so keep an eye out for missing coolant, wet carpet in the front footwell. You're likely already familiar with the bread clip trick for shimming the clutch on the AC compressor (I prefer the zip-tie method). Oh and keep that PCV system clean.
Lastly, you might think about a drain/fill of that transmission, for the resale value. The M56 in your car is sought after by a certain community of Volvo owners. The rest of your car could turn to dust, but the trans and third pedal will remain valuable as a "manual swap".

Best,
Will


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XC60 / Odyssey