2002 Honda Accord F23Z5 (2.3L)
First off the P1259 code is hinting at low oil/oil pressure or a faulty vtec solenoid. I've confirmed through voltage, resistance and continuity testing that the solenoid and its harnesses function as they should. Everything mechanically is also fine as the plunger moved smoothly (even without any oil) and the solenoid made an audible click when directly applying 12v to it. Also replaced the gaskets since one broke upon removal.
So the vtec solenoid seems to be working, now I'm guessing it's low oil pressure seeing as the oil level is fine. I don't know what oil was put in it last, but it was done in january along with an oil filter and has been driven very little since then. The oil is a good amber-ish color.
General issues with the engine which I feel could be related:
Huge lack of power (originally 154hp, feels like 40 at best, not because of limp mode as it is weak before it enters limp mode).
Difficulty running and starting (especially when cold, it'll stall unless you give it a bit of gas).
Vtec doesn't engage and bogs down at 3500-ish rpm (only happens once you receive the CEL when having gone past vtec engagement rpm range and ECU decides to go limp mode).
Possibly an excessive amount of air pushing out the valve cover. When warm, the engine idles from about 650 to 750 when removing either the PCV valve or oil fill cap (although I've checked the PCV valve which seems fine).
Things which have been changed in relation to this problem:
Oil and oil filter (since it was replaced for this reason, the previous owner likely made sure to put in the correct oil)
Idle air control valve
Spark plugs
I'm wondering if anyone else has had a similar situation where P1259 is due to low oil pressure and what their solution was (no oil pressure warning light btw). Any help would be appreciated!