Gripless

F*** you must have a spare parts bin... Depends how sick of the issue you are but if you swap one coil at a time you'll know which is the problem. mark the plugs with which cylinder they came out of. Masking tape and a vivid works so you don't mix them up for later inspection. Or easy for smart people to see in photo if you post one. thats a high idle! Not sure what caused that... Does your car have an idle control valve? Did the idle start hunting or was it rough when the issue started? Idle stepper motor maybe shorted. Again not familiar with Subaru just guessing from other cars. 2500 is the cold idle temp isn't it (think that's what my one does)? What's the Ecu think the water temp is? That would alter fueling a could fowl plugs etc. again some of the smart people on here maybe able to tell you more about the Ecu side. only time I've had idle that high was throttle not sealing when I ran a bored out throttle, but could be throttle position not reading correctly. Should be able to see it if you have a cable, even a cheap one can read to OBDII which may have TPS.

Is this coil over plug or common coil? Could be coil drawing too much, a broken lead wouldn't increase draw I don't think just have failed spark. Not sure how to test that other than swap it out. Got any Subaru mates that could lend you a coil. Maybe use IR temp gun on a known good car vs yours. Even that may not show enough difference due to their location. Unless you tested the temp without running the car. Could still draw a bit more current even without firing. Could wait until you have two cars cold and just turn key to on and not start and see if coil heats up a little more on your one. But now I'm really guessing or making S*** up. if it's coil over plug then one spark plug could look different. Black art of reading plugs, need an old school v8 guy for that. is the impedance the same as stock injectors. See still know nothing about Subarus... Yet.

Not familiar with Subaru Ecu so no idea how they store or process fault codes. Sounds like it's running down a list so either to got a whole bunch stored or the sensors are all failing. Since you have so many faults, you have enough faults that you need to look for a common cause. Errors can happen when the sensor fails or they are outside the expected range. that range isn't always as much as the sensor itself can go, just what the programmer set as the expected range. Since the only common things I can guess at are the Ecu, loom and the alternator. check the voltage at the Ecu and its grounds. Check the voltages or resistances of the sensors, you'll need a service manual which someone here will have a link too. Check the main loom for wear and damage, main plugs and firewall. I'd unscrew the Ecu and check inside to see if anything is leaking or corroded. Was car imported from Singapore? not sure how you check but water damage and re-compliance. someone on here will know way more about how the Ecu in Subarus deals with faults etc.

What boost is it running? Just waste gate or bleeding off to what? Could it have been reflashed or chipped by the previous owner? Or not tuned since the cat less down pipe (quick look at your old posts) that could explain the boost ramping. map and o2 both could be boost/heat related as, guess even same with plugs. Other alternative is bad ECU from aging like capacitors (*cough* Mitzi issue) or alternator spiking (only as topic already about bad alternator today) Again I know nothing about Subarus. Just asking some questions.

@Jono24 that is sick. 10k US for a block! Seen plenty of billet v8 blocks cost that much, but damn.

If you're replacing alternator then that maybe the only fault, can't see half of what's wrong with them without an oscilloscope. Check the current draw specs on the fuel pump at higher pressures if they list them and injector impedance is same as stock. If the engine has ever been out I'd still check around the main connection points, never know when someone forgot to unplug something or it got caught up during removal. Beers and late nights make for strange electrical faults. otherwise fingers crossed it was alternator.

Not sure what the main engine fuse runs further down, but grab a wiring diagram and look at the next level of fuses downstream. have you upgraded any electrical component that run off those i.e. fuel pump, coils, injectors, Ecu etc. guess at the least the voltage has been checked and are ok from alternator? Won't always show on digital multimeter but good start. when you replaced the fuse did you just get the same value or check the manual and confirm cover to make sure it was the correct one to start with? Could be lucky and just have a fuse that's to small. is the rest of your loom tidy? No shorts from unterminated or poorly joined cables. other free things to consider is anything electrical cable or component running closer to heat sources as the more you heat them the less efficient they run, which can increase current draw. Disclaimer: I know nothing about anything, ever.

Not in subaru's but if the holder clips are loose any vibrations can cause miniature arcing and that heats things up. The same will happen if the wiring loom isn't crimped into the clip underneath as well. has the loom been out before and are you missing and grounding cables?

Suburb or region?

Also same with the linke, maybe if I set Facebook to French?

Installed a new battery in the remote. Yip big job I know.

Given you had a pile of spare 'must spend on subbe' cash what interesting, different, uncommon part would you get. Something like Carbon fibre PST driveshaft Or Cosworth 2.2L Stroker kit Feel free to put a reason behind the choice...

Maybe go nuts?

Thinking of buying a earlier WRX to modify. Something around 96 onwards. anything I should look for that goes wrong or where they have rust issues?

Some 80s Japanese one at that. so much effort to remove parts and paint them cleanly. They must really love that colour scheme.