There are a couple of things that could cause this. First is a faulty servo or even a leaking vacuum line running to the engine.
We need to check this by checking the voltage going to the servo and find out if the ECM is commanding it off or it is just losing vacuum and disengaging.
https://www.2carpros.com/articles/how-to-check-wiring
https://www.2carpros.com/articles/how-to-use-a-voltmeter
The next likely cause of this is an ECM but this sounds more like a vacuum issue.
Take a look at the wiring diagram below and let us know what you find with this but if it were me, I would look at putting a servo on it as this is the likely cause of this.
Thanks
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Sunday, March 20th, 2022 AT 8:12 PM