Nice work.

The 1-1-1 codes are good.
I haven't memorized the other codes you reported but if the reference says they're "OK" results then that's good. It also indicates the OBD system is working. OBD wouldn't return "OK" test results if OBD had failed. Would return no results or would give you bad news.

You're absolutely right to go ahead with replacing the fuel pump regulator. Benstein and pageda already figured that out. I think they already described the failure mode. Leak in diaphragm of FPR lets the engine vacuum suck in huge amounts of raw fuel. Not enough air to combust that huge amount of fuel. Plus fuel getting into the engine oil via the piston rings, that's bad for everything that needs lubrication.

Definitely change the oil; we're sure it has gasoline mixed in. I remember my first oil change, on an old Ford V8. I could have used a few tips. On the 240, if your arms are longish, you can reach the drain plug lying on your back without lifting the car at all. Drain plug has a copper crush washer gasket; don't lose it. Get a new one (or a few) in advance if at all possible. Volvo dealer or parts store or fcpgroton.com. Less than a dollar.

If this is your first time, try loosen the filter by hand first, even before draining oil. Just to test that it's not stuck. Reach in from over the fender, not from below car. If no luck, put on old leather or rubber gloves for a better grip. Watch out for the wires between filter and alternator. If stuck, resort to a filter wrench. They can crush a stuck filter, that's messy. 10-30 oil for locales with winter. If you find that the car leaks oil, go to 15-40; you'll still be OK for winter.
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Sven: '89 245 NA, 951 ECU, expanded air dam, forward belly pan reaches oem belly pan, airbox heater upgraded, E-fan, 205/65-15 at 50 psi, IPD sways, no a/c-p/s belt, E-Codes, amber front corner reflectors, aero front face, quad horns, tach, small clock.