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It's a narrow band sensor. It only reads 14.7 AFR and has an EXTREMELY non-linear response. "Spec" and "Book" and all that nonsense is to be considered but only within the confines of what the manufacturer's motivations were for publishing it. First and foremost and in some respects the ONLY thing that mattered to them was Emissions. NOT Economy, NOT Performance, NOT NOT NOT. The FIRST rule of tuning - Give the engine what IT wants. It might idle nicely at 14.7 - but it might not. It might want a richer idle - especially if it's worn (likely at this age), or modified. It EASY to tune idle speed and mixture - you alternately adjust speed, mixture, and timing till you hone in on what the ENGINE wants - NOT what you want, NOT what the spec says, NOT what other people say it should be - NOT NOT NOT. Additionally - you won't be able to get any transitionary data from it - your DVOM is too slow and you aren't recording it - your pump shot and your WOT mixture will be WAY too rich to be anything meaningful on the narrow band sensor - it will just be 950 mV and then swing to 50 mV when you decel. It will be a useless swinging pendulum of meaningless data. Because the non-linear response of the sensor means at anything that isn't between 14.5 and 14.9 the readings change so rapidly with such tiny changes in mV that there's no resolution to the data and it's useless. The sensor was designed for a high speed computerized closed loop - wherein the computer responds by counting cross-counts through 0.5v and it is desirable for the mixture to "dither" above and below 14.7 in order to "charge" the catalyst. The computer only cares about the sensor telling to add fuel or subtract fuel - in a dance it calls closed loop. This results in the dithering behavior and is by design. The narrow band sensor was designed SPECIFICALLY for this purpose - to facilitate closed loop operation by computer. It was NOT designed to be a tuning tool. That's what Wideband Sensors are for. GD

Why not just fix the EFI? They are quite reliable and simple systems. GD

Did the battery die or was used until completely discharged at any time? Or maybe the car was jump-started? possible the ECU has lost its 'zero calibration' from the throttle I guess. There is a zero re-learn procedure. maybe someone more familiar with the newer cars will respond.

I’ve repaired a ton of front impact subarus. Never seen a cracked crank so maybe yours was worse than I’ve seen. Otherwise it’s not hard to get one back on the road. replace those parts and go. On some I’ve even just twisted and banged the top radiator support back into place - it’s thin and not significantly structural. So if I need a quick repair or it’s a rusty old Subaru not long for this world I just twist and bang them into place. You might be able to do that to do a minimal repair to get it running/driving before you decide to get into all the body work. hoods too can sometimes be banged And pulled back into usable submission too. But this impact sounds too big for that - usually something like a deer hit can be bent back to shape until you find a replacement

Geez that second pic of the pulley is pretty full on! I hope you find one, I’m sure someone will have one of you can’t find it on a parts site. It might come with a whole engine... Cheers Bennie

Had a similar situation happen to me but my pulley wasn't broken in the back like yours. Engine ran fine afterward, I didn't perform any in depth inspections. I would be checking everything electrical at this point. Check Car-Part.com for the pulley, plenty of listings last I looked.

You can’t see the friction surfaces without disassembling the shafts and gearsets. Not an easy task I reckon (I’ve not done this). With synchros you’re looking for some roughage on the friction surfaces. They stop working when they’re smooth and don’t create friction to slow or speed up the gear that the driver is trying to select. That’s when the crunch happens same as when changing gear without the clutch and you don’t rev match properly. You could pull the synchros and have them lightly bead blasted - I’ve heard this is a good method to bring them back to life. But the effort (or f’-it) to get the synchros out usually isn’t worth it. Cheers Bennie