Wow, no year stated,
now CC size of engine stated. huge numbers , all diffr.
Corollas sold over eleven generations, pick one. and state it.
sorry no one can , give zero inputs. what exactly and what year. and engine.
1: if it over heats (relic dash guage) use a pyro IR gun to find the truth there. costs what $15?
if it is overheating the engine will not idle right. how cound it.
so work overheat first.
that idle deal is called surging, (or hunting)
not only that , they used CARBs then EFI if many kinds.
so cant comment more.
the C >>> H cold and hot cycling is due to air in the system
on the cold engines, remove the rad cap ,see all that air, replace the air there, with 50% AF coolant. if motor overheats air can land there too. check for all signs of overheating. first. if the expansion botton on the side, is missing the internal hose it will suck in air and will in a week , cause the radiator to go lower and lower with fluid. this must be corrected. if thermostat is up side down same if bleed hole in same is not uphill same. it allows air to be trapped.
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SOURCE: No Heat in 99 Taurus
Just finished fixing my daughters 1999 taurus heat. It would blow warm only when running down the road. At idle it blew cold. I started with replacing thermostat, and water pump because they are the easier fix. Still did not help. Then I replaced the heater core. A daunting job but not that hard to move the dash slighly out of the way to replace. There is a good write up at tarusclub.com. After that, heat was better but at idle, it would still blow cool sometimes. Researched and found answer. Park car on the steepest hill you can find with front of car up. Start car and take off reservoir cap. Let car warm up and keep rpms about 1500. After a while the fluid will come running out of the car and all over the place but it will bring air bubbles with it. Reduce rpm, add more fluid and repeat about 3 times. It will make a mess but after that, the heater works perfectly. We get heat long before the temp gage indicates any and it never blows cold unless you lower the temp.
SOURCE: 2004 toyota corolla idle jumps
If you dont have any trouble codes, this usually occurs when the idle air control valve (IAC) is going bad.
SOURCE: Toyota 1999 Corolla,low idle,my corolla idles at
adjust the accelerator cable.
Testimonial: "i thought the idle was ecu controlled,but i see what your saying,ajust cable stop.ie allen screw with locknut to bring up revs.thanks"
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