1 Lucky Texan

while the car is idling normally at night with the hood up, you could spray the spark plug wires with a plant mister of water. Watch for the engine to miss and maybe see some arcing on the coil or wires. New plug wires would not be an unusual swap on any 17year old car. OEM wires only, many folks report issues with other brands.

is the car new to you? what's its history. we never want this to be HGs, but, it usually is. OEM style thermostats? it matters. also, you might try 'burping' the cooling system with the nose of the car up (ramps or an inclined driveway, etc.)

make sure the a/c condensation drain is open and the cabin air filter is not wet or growing mold. do any passengers complain of problems? new ANYTHING can outgas vapors at first. Cars can be a little worse as they are closed-up areas and contain a lot of plastics. Perhaps an allergy/asthma specialist could test you for substances commonly found in new cars?

bad sparkplug wires, maybe coil, can do this - sitting overnight allows a little condensation to form, causes missing until engine heat dries the high voltage parts out. OEM wires are the only ones with no complaints, other aftermarket brands often won't work well for people.

our 03 H6 OBW has one. the gasket can leak so, cleaning the area and watching for a leak is a good idea. The nipple that the filter screws on to is what holds that on and it takes a deep 24mm (maybe 26mm ?) socket. You could try tightening it first, might slow down the leak if that's the source.

you might be able to coat some suspected parts with different colored crayon. assemble, spin,remove and inspect.

on a 96, is the abs tone ring part of the axle?

any 5 year old car could have problems. Subarus are no exception.

well, there's no doubt good first-hand diagnosis by a trained tech with proper equipment has value. but, given some of the unknowns with a new-to-you used car - there's not much could be lost in double checking some common areas where confusion or laziness could lead to improper parts, fluids or installation techniques that might cause issues. Some things on these cars can be cheap aftermarket - like knock sensors, other stuff NEEDS to be OEM or specific suppliers like spark plugs. And, due to the AWD design of the transmission, some techs can be easily confused and drain/fill improper fluids. Front diffs drained and dry, or filled with transmission fluid, etc. not sure your level of DIY comfort, there are online guides and youtube videos showing how to service most of the areas we've discussed. You can also post a request in a new thread for a soob-experienced indie. mech. near your city. That might be a good place to take the car when you've exhausted the 'easy' stuff.

read a LOT of posts across multiple Forums for years - only ever read of one bad coil-on-plug type coil. very uncommon if your car has c.o.p. type for one to be bad. Swapping it with another cylinder to see if the misfire follows would bea good diagnostic procedure. if someone serviced the car and installed other than NGK plugs - I'd change those before any coil. if there is oil in the plug 'tubes', could be a leaky valve cover gasket. are you getting a CEL for misfires?

Impreza Outback? if the VIN starts with a 4, US, if with a J, Japan I think. I suppose a u-joint or other drivetrain problem could cause what you're sensing. Seems early for that kind of failure unless the car was abused.

from whom did you buy it? If there's any chance someone unfamiliar with Subarus worked on it before the sale - they could easily have used an incorrect fluid in the trans. 3 drain/fill/drive cycles with Subaru ATF-HP (or w'ever they call it) would get you around 85% new fluid I think (I might be a little off, you have a 5EAT right?) also, the car MUST have 4 tires that match, same brand/model/wear level. The more the tires vary from each other, the more likely you will have torque bind.

when you have the timing belt off - check all the idlers. None should wiggle and, ideally, they should not spin like skate wheels. the toothed idlers sometimes have very worn bearings.

keep your soob rotors unless they are below the minimum thickness marked on them or are 'damaged' in some way. Just be a little careful on your first 3-4 stops. The new pads will quickly wear-in to any waviness on the rotors. I like Centric Posiquiet ceramic pads. OEM pads are Akebono ceramic and very good - just a little pricey. probably any name-brand semi-metallic or ceramic pad will work.

how long since the last timing belt service?

when was the last timing belt system service? maybe it slipped a tooth? bad knock sensor will often not show a code and kills performance.

how long since timing belt system was serviced? could have slipped timing a tooth or 2. I would rule-out possible blocked exhaust. seems like w'ever happened had sudden on-set , but, as said, there are several possibilities.

many people rebuild the solenoid - parts are affordable. I've seen kits on ebay and there may be a coupla youtube videos that show how to do it.

some folks adjust the p-brakes at the handle, might have to take a look under the console? fairtax, is that possible?

what happened to the present rack?

I suppose there's an extremely unlikely internal failure of some type (what???) that might lock-up something internal to the trans or front diff - depending on 'what' is the trans issue. given your post though - I think it's fine. ATF will get overheated, but front diff is splash lubricated. viscous unit ??? I dunno

are you freakin' kidding me? a SWITCH went bad and they recall the cars? HAHAHAHAHAHA*cough*HAHAHAHAHA!!! my secondary air VALVES (not switch) have been frozen shut for 6 years I think now. crazy, I had to kill-off 14 DTCs with ecuflash. i DID keep my original ROM image, but, even if they replace the valves, what if they just freeze shut again in 4 years? got a link to info?

good point, if it's the NGK copper, probably done-in at 30-40K . But many newer models seem to come with the platinums installed - definitely check into that.

even temperature and tire pressure can affect mpg. I't s something that needs to be tracked over multiple tanks under very similar weather and road conditions. FYI - according to the time side of the maintenance schedule, you should have the timing belt system serviced.