something is making the idle speed surge to fast back to normal?

1991 TOYOTA PICKUP

140,561 MILES

AIRFLIGHT

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When engine is first started something is making the idle speed surge to fast back to normal.After a few minutes the idle speed is normal.I also notice this when the AC and heat is turned on.The vehicle is a 1991 Toyota truck 4cyl,4x4 5 speed manual transmission with 140561 milage.thanks

Sep 23, 2011 at 11:49 PM

SQM

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Hello,

It sounds like an issue with the idle air control valve. Toyota calls it idle up valve.
This valve controls the engine idle speed. It allows more air into the engine when the A/C gets turned on to keep with the extra load.
Over time the valve can become dirty and have air flow restriction, this can impact the idling quality of the engine.
Sometimes cleaning that valve can improve the idle.

Here are couple of helpful articles:

https://www.2carpros.com/articles/how-a-idle-air-control-valve-works
https://www.2carpros.com/articles/idle-air-control-valve-service

I attached diagrams for your reference.

Please let me know of any questions.
Thank you.

Images (Click to enlarge)

Sep 26, 2021 at 7:32 PM