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1 pointCould potentially be a leak in the intake manifold. On 9th gen Corollas like yours, there was a TSB for an updated intake manifold gasket that sealed better against the composite material, especially in cooler temperatures. But those tend to "cycle" between fast idle and normal idle constantly. If it is just fast idles right after starting up - but eventually coming back down to normal idle range - sounds like it could be the new normal to me. Noticed my RAV4 and Corolla doing that more and more when the weather is colder - chalking that up to the amount of miles on them (almost 300k on Corolla, 105K on RAV4).
1 pointyou will need a 3/8" drive 5/8" spark plug socket, an 8" extension, and a 3/8" socket wrench (ratchet). if you have a '99, all you need to do is pull the spark plug wire boots (4 rubber things on top of the engine with 4 corresponding wires, one for each rubber thing) all loose (but don't pull them all the way out), then once they've all been loosened, pull the whole bunch out leaving the wire loom clips attached so everything stays tidy.. put the socket, extension, and ratchet assembly all together (it only goes together one way), then make sure the directional switch at the head of the ratchet is set to loosen (you will know it's set to loosen when you put the socket down into the spark plug recess and turn counterclockwise and you feel resistance. if it clicks, turn the selector the other way. turn the ratchet counter clockwise until it feels as if the spark plug is loosened completely... if it is, the retaining bushing inside the socket will hold onto the spark plug enough that you can pull it out of the engine easily. Do this for the 3 remaining cylinders. You should have 4 old spark plugs sitting somewhere now. unhook the ratchet from the socket / extension assembly. take one new spark plug (they're usually gapped pretty close to spec so you don't have to really worry too much about that) and insert it into the socket until you're sure it won't fall out easily... gently and carefully insert the spark plug into the spark plug recess until you feel it reach the bottom. turn the extension by hand until the spark plug feels like it's snug. it should turn at least 4 full revolutions. if it does not, it may be cross-threaded... turn it counter clockwise to remove it, and keep trying until it's obvious that it's screwing in correctly. pull (slowly) the extension / socket assembly off of the spark plug, and insert and hand-tighten the other three spark plugs. NOW!! re-attach the ratchet to the extension, turn the selector the other way so that you can tighten the spark plugs... put the socket down into the first spark plug recess until you feel it engage with the spark plug. turn slowly clockwise until you feel steady resistance.. at this point, give it about 1/8 of a turn. it should be tight. make sure you hold the head of the ratchet perpendicular to the engine so it doesn't wobble while you're tightening the spark plug, or you may crack the insulator and have to buy another spark plug. once you've gotten all of the spark plugs tightened, re-insert the spark plug wires into the tubes (they should only all go on one way) and push them down till you hear them click into place. try starting the car. if it starts and runs smooth, close the hood... you're done. If not, and it ran before.... You should not work on a car, ever. Pay someone else to fix it, and sell your tools.