1 Lucky Texan

Sometimes, selecting a lower gear reduces strain on the engine and increases coolant flow. Make sure debris/dead bugs hasn't built-up between the condenser and the rad.

are you keeping the car? If so, get the KYB. Very likely you also need strut mounts. KYB may have some assemblies now, but I forget what years.

yeah, that sounds horrible, but , being across all cylinders makes me wanna say it COULD be slipped crank timing. That is, when the valves are fully closed, the piston is not at TDC.

check timing? maybe off by a tooth. They car run but be down on power. if it seems like the car hasn't had great carein the past, certainly possible to have more than one issue.

very unlikely, 'warped' (usually uneven deposits from pads, extremely rare to actually 'potato chip') rotors would be felt when applying brakes. Not to say stuck calipers could cause issues. https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjRosfmsZbxAhXDG80KHWfmBDMQFjAAegQIAxAD&url=https%3A%2F%2Fcentricparts.com%2Fgetmedia%2Fbd69395a-b65c-481d-93f7-b26b1bd0638d%2FCentric_and_APC_Technical_Whitepaper_B1-Warped-Brake-Disc-8-2018_1.pdf&usg=AOvVaw2Syl_CnageQ47I6fsJZy3W check toe in the front. I don't recall the first page but, inner tie rods, ball joints OK? Maybe bad steering rack bushings could do this???

fluid level OK? did Mom's car sit unused during the recent slow-down such that there could be rodent-chewed wiring or???? just hoping it isn't internal......

triple check breather and PCV hose routing I guess. in the 'old days', oil smoke at startup, and on the highway after - an abrupt foot off accel. , wait a few yards, then foot on the accel. induced smoke puff - often was a sign of bad valve seals I think?

smoke smell fuel-ish or oil-ish or sweet like coolant? if you suspect fuel is getting in the oil, don't neglect oil changes. maybe PCV valve is stuck open?

drain the oil, swirl a magnet around and see if you get metal? or send oil in to Blackstone labs?

the only way I got an axle out of my daughter's Impala hub was a little heat and penetrating fluid - after much force with 3 jaw puller pushing on the axle and an impact tightening it and a big hammer, etc. 20 seconds of propane at 6 and 12 o'clock. didn't car about any rubber as everything was getting replaced anyway. Becareful not to start a fire. car was rust free too. My guess is, there's enough moisture can condense or wick? on the splines over the years to make rust due to limited chance of drying out the tight space?

hmmmmm, I have no experience with models this old, but, have you recently serviced the trans? Did you use synthetic lube?

Man, I could not even find a good video on using manifold gauges. I use the them for vacuum application and charging, etc. But the whole pressure ratio thing is hard to discern for me. I can tell you, the system can make a 'hooting' noise if it is overcharged so, there's that. It is sometimes helpful to use a box fan to blow into the radiator too I think.

Just didn't know if the avls/var. valve system has them.

Ido - any oil screen issues on this car?

until you get into dual climate, most cars have 3 'flaps' with electric servo motors/controls. A flap/door for fresh/recirculate, one for defroster, and the one I think stuck or failing on your car us usually called the 'blend' door I think. FSM or some diagram from an image search might show you it's position in the car.

way to stick with it.

Gen 3 Outback Legacy headunit radio a/c climate combined this thread may have some interest for people fighting a bad radio in a Gen 3 https://www.subaruoutback.org/threads/jdm-hvac-alpine-stereo-install.533355/#post-6114611

if the 'frequency' of the shaking is closer to 4:1 with wheel rotation, than 1:1 = driveshaft.

^^^^ bad tires too can cause that, swapped wheels back to front?

I have an appointment to get some General G-Max AS05 or w'ever they're called on the WRX. Kinda had to play the sympathy card at the last inspection to get them to pass it.

Man, I dunno about an axle causing that type shake but, I might try just grabbing the axle and try jerking it around, do the same on the other side, go back-and-forth, maybe swap whichever one seems to move the most?

just realized - boots - so, pay no attention to me......

way to stick with it!

yeah, not unexpected to be tight in there.....if you could get something in there, just do it blind, assemble and try, then pull it out and try some other spot. Not as ideal as someting with easy access and powered-up on the bench....just grasping at straws.....

' plunge shaft ' yeah baby