P300 is multiple cylinder misfire, and P302 is misfire cylinder 2. Likely either a fuel injection problem or a compression problem (or both). Most of the stuff you ran is hitting both the injectors and entering the combustion chamber. I don't know what kind of shape your engine is in, but the clearances are very tight in the 1ZZ-FE so if something big enough got dislodged from the solvents, it could have found its way into the injection system or in the combustion chamber. You've already ruled out several possibilities (unfortunately, many of them are the cheapest and easiest to fix).
I'd still do a compression and leakdown test. Cylinder 2 might be dead or show very little compression, but only a compression test will tell.
I have a badly sludged 2000 VE 4 spd auto that's also burning oil (about 1 quart every 1,400 miles). It was sludged and had a leak when I bought it, plus lifter tick. Leak is fixed, but the consumption continues. I too nearly resorted to some drastic measures and considered, at various points in the 10,000 km since I bought it, many drastic measures including most of the things you did. In the end I ran a series of very short 2,000 km dino OCIs which initially had no effect. 1 Regane cycle on a full tank cured the lifter tick (I don't recommend this in your situation), and replacing a gummed PCV valve began to very slowly reverse the sludge process. After another 2K OCI on dino, after replacing the valve, I switched to Pennzoil Platinum and have since run another Regane cycle (3k after the first one). I'm going to run the PP for 3-4k (sticking to short OCIs) and introduce about 3 ounces of MMO into the fuel refills, and another 12 into the crankcase toward the end of the OCI.
I've read success stories of people curing, or reducing, consumption by using MMO in the gas (it has both upper cylinder lubricating and carbon cleaning abilities, leading me to believe it succeeds by freeing up stuck piston rings - part of my problem). I'm planning about 4-6 back to back treatments with MMO. At the very end of the OCI, right before the OC, I may also do a piston soak with 1 to 2 ounces of MMO in each cylinder.
I've had the MMO bottle for about a week now and still haven't opened it. I can see the sludge reversing (priority 1) now, but I'm hesitant about introducing potent solvents into the crankcase out of a concern that too much, for too long, will either clean too well, or break up something big enough to create a blockage and do damage where there is none. PP and short OCIs are safest, MMO maybe as a catalyst at some point (in a weaker than typical concentration, as this will avoid thinning the oil out too). MMO in 3 ounce doses will go into the gas tank next fillup, but there I'm playing it safe too (5 ounces is the recommended dose).
Just my own approach with solvents. I could achieve an even more potent effect on the upper cylinder by using ATF in the gas instead of MMO, and contemplated that for awhile too before dismissing it as a bit too risky in a modern fuel injected engine. Seafoam through the brake booster was also debated for awhile too, but dismissed as well as being too harsh (and therefore too risky).
Except for cleaning the MAF sensor and throttle body manually (both of which I've also done), I consider each of the measures you've tried (individually) as too risky for anything other than an old beater that I was planning to scrap, dump, or just didn't want to put any money into. Others have had success with things like Seafoam, but I guess I'm ultra-cautious with solvents. I don't consider varnish bad unless it develops into sludge, but mild cases of sludge can be dealt with by shortened OCIs.
Anyway that's a bit off topic. Hopefully the damage isn't too serious. Absolute worst case scenario you may be looking at a small block rebuild, but hopefully its not anything requiring that kind of intervention.
-Spyder