OBD = on board diagnostics. Prior to 1996 there was no standard and each car MFR had their own systems.

For your 4runner, there is a pair of pins you can jumper with a paperclip and you can count the flashing lights to determine the code(s), if any.

Google is your friend.

If all of this is still above your head after an hour or two of internet study, then go have a chat with your mechanic. They will know what to do.

Overgapped or worn plugs can misfire at high rpm.

Pro tip: if you have CEL codes, always put them in your OP so folks like us have a better clue what’s going on with your ride.

Yes that’s possible too.

Might not hurt to throw a bottle of Polyetheramine (trade name Techron) in the fuel tank, follow directions on the bottle.

In my personal experience, the really bad mechanics will play anyone otherwise uninformed regardless of gender as long as they have a credit card.

Presuming that your mechanic is incompetent/dishonest, my advice is:

Stop work at your mechanic and have the car towed to the dealer and pay them whatever to get it fixed properly.

Dealers don’t fuck around with people’s brakes … they are way too big a financial target and lawyers will line up to sue them blind if someone gets hurt because of a botched brake job. If your dealer finds damage (stripped bleeders?) ask them to document it for you. Then if you choose to seek relief from the mechanic you’ll never use again, you have a bit more than just your say-so.

Check the purge valve.

If your car has an Idle air control valve, check it too.

And don’t overfill your fuel tank.

https://willtheyfit.com/

^ try it

If you know how to use a multimeter and understand ohm’s law, then do a voltage drop test across the fuses until you find the circuit(s) with parasitic drain. Use a chart like this one. Then fix what’s wrong with those circuits.

If you don’t, then find the best automotive electrician in your area.

Buy a battery tender for $100 ish with a de-sulfating cycle (I’m a fan of the Ctek MXS 5, but there are plenty of other good ones out there). Put it on the car and use the “recondition” mode. Then let it finish it’s charge cycle. Might take a couple days if the battery is discharged.

If it faults, replace the battery. If it doesn’t then go back to your normal life and stop worrying about it. Repeat the battery tender treatment every 3-6 months or whenever you do an oil change.

Your local LAPS might rent you one for a few dollars… or for free. Or you can get one at Harbor freight for a few more.

Don’t drop big $ on something you’ll use once.

I’d say your experience is typical for twenty-teens-era korean car that’s driven easy. I’ve driven a few Hyundai’s >100kmi on original factory brake pads and discs. Still had >5mm on the fronts at 100km when I changed tires on my last one and rears were still “new” and operated perfectly.

In most cases, when the pads are worn the built-in “squealer” will wake the dead with its shriek … like fingernails on a chalkboard.

If it’s ONLY vibrating while accelerating, not when coasting, and vibration gets worse & faster with higher vehicle speed… then have the CV joints in the axles inspected.

taking off from a complete stop in second is pretty slow

Why are you not using 1st gear? (rhetorical) The 3VZE engines are anemic enough without lugging it into 2nd. I owned one too.

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You test compression with a compression tester (see youtube). Might be able to rent one from your LAPS. You test running rich by watching the fuel trims (if the car’s OBD supports that and you have the diag tool). Otherwise inspect the plugs when you remove them for the compression test. Black/oily/wet plugs are sign of poor combustion and/or rich running, both of which may be confounded by bad spark. Grey color on plugs is normal (more or less). Plenty of youtube and other guides out there for this.

Because you replaced a cracked rotor cap with an old one, how do you know the old one isn’t contributing to the performance problem? Perhaps it might make sense to correct that and any other known issues (you mentioned you broke things) with the car BEFORE trying to diagnose a problem that may indeed be caused or contributed to by said old/worn/broken things.

Did you check for codes using the paperclip method?

with this

https://www.harborfreight.com/trim-and-molding-tool-set-5-piece-64126.html