There could be a couple things that cause this. The fact that the engine runs normally when it starts shows that it is functionally okay. The fact that this starts after it starts to warm up means we are most likely dealing with a sensor or PCM issue.
I am attaching a quick description of the run modes open and closed loop. Basically we want to find out which of the two sensors could be the issue.
If you have a scan tool that can monitor the o2 sensor data, that would be great. If not I would suggest unplugging the o2 sensors and then start the engine when it is cold and see if it continues to do this.
Basically the PCM will run off a calculated program like it does in open loop if it can't read the o2 sensors.
This means it will continue to run off this program even after it is warm which means it will not do this if the o2 sensors are the issue.
If this is not it then we will have to move through some of the items in this guide:
https://www.2carpros.com/articles/symptoms-of-low-engine-power
If it does not do it then we will need to figure out which sensor is the issue. We can test them using this guide or even just replace them.
https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor
However, let's do this first and go from there.
Thanks
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Sunday, August 8th, 2021 AT 4:53 PM