1 Lucky Texan

well, 1 & 3 do share a coil so, that was a good guess. did the wire boots on the plugs have oil on them? how did the old plugs look? also, have you checked for slipped crank or cam timing?

maybe pull the thermostat and test in hot water on the stove, make sure it opens smoothly at around 170 - 175* or so.

not sure - but do a search and read up. you def. want the Subaru turbo engine gasket s(or possibly one or 2 aftermarket) Multi layer Steel gaskets. And heads need light resurfacing. Probably do not want to do it on an engine that has had several overheating events or been severely overheated - possible bearing failure after expensive work would be a bummer. Some folks get junkyard engines, often low miles, and rebuild heads and timing belt system to swap in. there are discussions here, over at subaruoutback.org , probably some youtube videos, etc. for diy. I have never done it.

3 & 4 share a coil, maybe it failed? might also try a vacuum test - symptoms similar to clogged exhaust I guess.

diy? decent kits start in the low $100s . hiring it done, figure about $80-$100 and hour and - I dunno, 2-3 hour labor charge(3 is definitely high-side for an experienced mech. i think, depending on what other minor service is combined with the TB I guess?)? some places may get a profit on parts so - $400 ? call around, a good shop should be able to give a quote +/- 10-15% . if you post your city in a new thread asking for a shop, maybe someone will have a recommendation. if you suspect the car has a HG problem though, you need to confirm before putting good parts on it. I read a lot, but have much less experience than many folks here - I did the TB service on my WRX last year - found the toothed idler very loose, noisy and a little wobbly. about 8.5 years, but less than 60K miles! The pulleys lose their grease over time and can seize or fall apart. My belt tlooked great but 2 pulleys were going bad. Would the car have made it to 105K like the book says? - I doubt it very much from what I found. Glad I did the service. You also get a chance to look for oil weeping oil past cam/crank seals. Good time to throw new accessory belts on, change the coolant, put in a new thermostat.

thermal efficiency is better at higher temps, less likely to carbon-foul the plugs too. Oils are designed to be at 'proper' viscosity at specific temperatures ,etc. sure, specific engines in specific conditions might benefit from some change to operating temp. But keeping temps in the proper 'range' is best.

you must confirm the car has; proper coolant level in the radiator, not just the overflow and, correct subaru-style thermostat (with large wax capsule) I also have put small zipties to clamp the overflow tube to its nipple of the rad. neck. Puttin the front of the car up at an angle can sometimes help work air bubbles out of the coolant system. new rad cap might be a good investment too. typical HG failure will probabl;ly push coolant into, out of the overflow - may even see bubbling while idling after an overheat event. interference engine, if you are not CERTAIN the belt and particularly the idler pulleys are newer than about 100K miles OR 8-9 years, then you should do a timing belt SYSTEM overhaul.

most 'fairly modern' soobs use a 170* stat and it has a larger wax capsule (probably for the thermal mass/hysteresis) Stant's Xacstat model is probably OK too - it is built like the Subaru model.

you need the reverse-extender.

there are youtube videos showing how to use an infrared remote thermometer to measure exhaust tubing pre and post cat. If you feel the cat is working, you might try a new rear O2 sensor.

you try one of those extenders, if it prevents the code, go get your test, then continue troubleshooting. http://www.amazon.com/Blox-Racing-BXFL-00108-Eliminator-Adapter/dp/B000W1XX4M/ref=sr_1_fkmr1_1?ie=UTF8&qid=1441903416&sr=8-1-fkmr1&keywords=rear+o2+sensor+extender

first, clear the code and see if/how quickly it returns. I would never proceed too quickly on a a spurious pending code. double check for exhaust leaks - pre-cat. on a 2002, that code is not used to adjust any operating parameters. not that it may not indicate something that needs attention, just that, it's sole function is to say it thinks the cat conv. isn't working. Some people with otherwise perfectly running cars cheat the rear sensor with a resistor or an extension pipe (sparkplug extender w'ever) to avoid that code.

first - tires must be the same size/brand/model - and near each other in wear. second, automatics have a FWD fuse slot - under the hood. Put any spare fuse in there and see if the problem goes away. (I think on your car, it may be a little box on/near the right side (US pass.) strut tower?) If the problem goes away and you don't want to spend any time/$$$ on the car - you can drive in FWD mode. but, sometimes, the problem is a bad Duty C Solenoid, or, a wet clutch pack that is binding (I think some older soobs had an aluminum part that wears too quickly, there may be a steel upgraded part if you repair your trans - or you may need to install that part in a replacement trans?). some people shop for a replacement trans - often getting a used one from a junkyard with fewer miles. Some people repair their trans. any replacement trans must be the same final drive ratio. If the car is new to you, maybe a prev. owner put the wrong trans in it?

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hmmm....could be the car was restarted with the foot depressing the accelerator and it corrupted/confused the ECU's expectation for 'closed throttle' at the TPS ?? not sure it actually could be a good idea to clear the code, and re-start. Do not depress the gas pedal. The car may crank longer than typical as it will likely need to make adjustments to get to an acceptable a:f ratio and begin completing monitors.

yeah, probably a good idea to always meet strangers at the bank or in daylight at some busy area or an area under video surveillance if cash/goods will be exchanged. Perhaps bring a friend to observe if something feels 'hinky'. Trust your gut and do business in a business-like manner.

replacement trans must be the same final drive ratio. places like car-part.com or LKQ 'should' have inventory that's correct. Or maybe find someone on craigslist that is parting-out a similar model. just to be clear - all 4 tires are the same brand/model/size and near each other in wear right? critical on AWD cars.

H6 ? I see impact screwdriver recommended for all the timing cover fasteners - and make a cardboard template to store them on if re-using. start soaking them in Kroil, PB Blaster or 50:50 acetone and ATF. start that last week!

from what I've read - there is VERY LITTLE clearance on the other side of the trans pan and if it is visibly dented upwards, solenoids can be damaged, wring compromised, etc. might be an easy fix though with a new pan and solenoid set from a wrecked car.

battery cables frequently have hidden corrosion in side - under the insulation. Years of 'wicking' acid-laden moisture inside. Sometimes the cables can be felt to get hot when the trying to start. also, the 'other end of the circuit' can be part of the problem - the ground connection. many of us refresh ground connections every-time we are under the hood and spot one. There are usually some on the firewall near the pitch-stopper mount, some on the intake manifolds, usually on one or both fenders. take em loose, wire brush every connection surface fron and bacl, even the bolt. fasten them back down . I like to then smear them with dielectric grease. if the car has had lots of battery terminal corrosion in the past, or the cables get warm when starting - probably a new set of cables is called for.

was it a used or new replacement? what brand?

tranny? and rear diff ? those 2 MUST have the same final drive ratio or you will get torque bind. next time the wheel locks up, chock the other wheels and carefully jack that corner of the car up - see if the binding is released. Or, see if you can do slow, tight circles in a parking lot smoothly.

any work done or wrecks before this began? there's a very rare type of failure inside hydraulic hoses that can create a one-way valve.

so, you actually detect a vacuum when you remove the gas cap? seems like an evap hose may be clogged and, until the purge solenoid opens, you have low fuel supply. I suppose hooking a fuel pressure gauge up that you could monitor while driving might prove that theory. probably need to find the evap DRain hose. On many systems, there is a hose attached to a 2-way valve. It lets air out of the tank when fueling (or maybe when pressure builds up as gas warms?), but is supposed to let air in as fuel is used-up. probably a hose about the size of your thumb, coming from the charcoal canister area. Some cars like Mazdas attract spiders that clog evap hoses. i have heard of mud from off-roading clogging the hose. I suppose the valve could be bad......

a 5spd from a junkyard (car-part.com or LKQ ?) could be good option, but, must be the same final drive ratio as the present trans. Might find one with substantially lower miles. also, the drain plug does have a magnet. If there is more than about 1/4-1/2 teaspoon of sludge on it - or, even worse, 'chunks' - that might be a sign that a new trans is the best option.