Hi Bill,
If you feel a misfire at idle, it could be a few things. First, the components you mentioned above can cause it. Also, engine vacuum leaks, fuel pressure, a faulty oxygen sensor, and so on.
First, do you have a live data scan tool? If you do, I need you to check two things. First, let me know what the short-term fuel trims are, and second, let me know if the engine coolant temperature sensor is sending an accurate signal. For example, if the engine is at operating temperature, does the sensor indicate a temperature of approx 195°F?
If you don't have the scanner, we will need to check the fuel pressure to confirm it isn't too high or low, along with checking for vacuum leaks. Here are two links that explain how it's done:
https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge
https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator
Please keep in mind that the A/C places a heavy load on the engine, so pay attention to the engine's RPMs. Make sure they aren't dropping too low. That can cause a vibration that will resemble a miss. If you notice the RPMs are getting low, we will also have to check the idle air control valve. The powertrain control module should signal the IAC to increase idle speed to compensate for the added load.
Let me know what you find or if you have other questions.
Take care,
Joe
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Monday, June 7th, 2021 AT 9:22 PM