Check your charging voltages, if you haven't already. Check at idle with no load. Check again with a big electrical load. Check both while revving it up to at least 2000rpm. Check right at the battery, check at the + of the battery and at the - from the engine block. If you're not 13V+ all the time, it's not compensating for electrical load.
It seems very odd to have a code for something that wasn't part of the original set up. Is there a way to add it? Of course, they might use the same code for other means of detecting electrical load/alternator response. Low idle might mean no charging, might throw a like code.
Is there a Throttle Position Sensor? They can assume/calculate throttle position based off the MAP sensor, but not having a TPS on a lean-burn engine seems...silly.
I'm new to lean-burn, but reportedly the Insight can be forced in to lean-burn by backing off the throttle just shy of going into regen, and then re-applied, thereafter it will be in lean burn mode...if you're driving it gently for MPGs, and haven't tried it, try driving it like you stole it, with the o2 sensor plugged in, and see if it stays perky.
The other thing that comes to mind is that one of your cylinders isn't firing - weak spark and/or too little fuel getting in - and so the o2 sensor is detecting unburnt oxygen and throttling back the fuel on all cylinders in response. Very much like lean burn, just in an uncontrolled way. You could have a bad spark plug wire, a bad/dying coil pack, oil down the spark plug hole, or, the first thing that comes to mind, worn/over-gapped spark plug(s). I'd think running lean would make it that much more difficult to fire the spark plug, so I would naturally assume a lean-burn engine would have a smaller spark plug gap. But that's me, and assumptions tend to be the mother of all f'k-ups.
There's also the injectors. One of them could be stuck on, or not responding properly, or clogged enough that running lean means there's not enough fuel to overcome the poor atomization....bla bla bla. Way too many if's going on here.
Your MAP sensor, being on the firewall, rather than right on the manifold - if that's how the D15Z1 engine usually runs it - could be an issue. Wrong sensor, or there's issues with the vacuum hose going to it. Blocked/collapsing or leaking. Or it really doesn't like the delay caused by there being a hose between it and the manifold.
Right now...we know you have a code that points to something you say it doesn't use(which makes no sense), and you use to have a code 48...
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https://axleaddict.com/auto-repair/H...what-they-mean
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ok, that gives a different wording to what code 48 is. Sigh. Heated o2 sensor.
You've most likely either messed up with the wire you repaired - or one that you repinned - or you simply need a new O2 sensor. There's procedures to test non-wide-band sensors, there's probably ones for wide band too. The heated circuit is pretty dang important on these things, as they operate at a higher temp, so the first thing to do is to check that you're getting 12v power to the heated circuit pins, preferably in the right polarity, and that the heated circuit itself on the sensor is reading a proper resistance while disconnected. Don't know what proper resistance is, but infinite and zero resistance automatically mean it's bad.
Heated o2's run theri own ground wires for each circuit in it, unlike early/simple non-heated ones that get ground from the manifold itself. Test your resistance on the ground pins, all of them, to the block. Should be close to zero. Check that you aren't showing +12v on what should be a ground pin too, in which case you've probably found your wiring issue.
That being said, again, if you have a cylinder that isn't firing, it's dumping oxygen (And fuel for that matter) in to the exhaust, the o2 might be reading right, sees the oxygen, and automatically starts dumping more fuel in. Check all your ignition parts, and check your spark plugs both for gap and the color of the darned things, looking for rich mixture or even wet from a plug not firing.
Hows the gas mileage with the o2 disconnected?