problems with my corolla 91.

Greetings friends, my problem is that my 1991 Corolla sometimes feels like it's idling too high, and other times it idles too low. This happens under the same driving conditions. I've taken it to the mechanic several times, and he's checked the coolant temperature sensor, ignition, airflow sensor, fuel filter, vacuum hoses, fuel pump, generator, etc. This is a very strange and annoying problem because it happens every time I stop and the car is in low gear; I have to put it in neutral for it to idle a little.


My vehicle is a 1991 Toyota Corolla, fuel injected, American version.

I would be eternally grateful for your help. Thank you.

Hi.
I see you've already done several checks, but I'd like to know what other changes you've made besides those. Also, is your car automatic?
What I can tell you is that a common symptom is a problem with the idle air control valve. Cleaning it is important, and another thing you can do is replace all the gaskets in the intake system; one might be broken. You can start with that and then let us know.
Good luck...

First of all, thank you for your interest in my problem. Thanks for your support. Regarding the vehicle, I've replaced all the seals in the intake system, including the injector seals, and I've also changed the air filter. My vehicle is automatic. Finally, I'd like to ask you to please explain what the idle air control valve is, as I'm not familiar with it. At least tell me where it is and what it does, because I'm a bit of a novice with this and I'd like to learn more about my vehicle. Thank you.

The idle air control valve (IAC) or stepper motor is a valve that regulates the idle speed. It's located in the intake manifold where the throttle body is. It delivers a greater airflow through a bypass, or a lesser flow for cold starts. When this valve is dirty or malfunctioning, it becomes uncontrolled, and the vehicle may run fine at high speeds but tend to stall at low speeds. One symptom of this valve is seeing the tachometer needle fluctuate on its own in neutral, going up and down; that's a sign.

Thanks again for your input. I wanted to let you know that your answer is very helpful because it closely matches the problem. I'll put your advice into practice right away to see the results of cleaning this valve, and I'll let you know how it goes. Thanks.