Intake manifold

If this is leaking, then you will have what is called a vacuum leak. This is basically air coming in after the sensor, so it is not being measured and causes poor or rough running.

To test for a vacuum leak, we need to use this guide:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

There are a number of ways to test this, but the best is to use spray cleaner and listen for the RPM to raise and that indicates it is leaking and pulling in air.

Please run through this and let me know if you have questions on it. Thanks