Your car should be throwing a check engine light if there is an issue with anything relating to emissions. Running rich would be one of those conditions that should trigger a CEL.
You will use the short and long term fuel trim gauges along with the air fuel ratio to evaluate a vacuum leak or other problem with air and fuel delivery.
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For a suspected vacuum leak, note the fuel trims at idle and increase engine speed to 2500 RPM and hold. If the STFT immediately decreases and moves to acceptable levels and the LTFT slowly starts to come back down, you have a vacuum leak. After the repair, reset the KAM and start the vehicle. Monitor the fuel trims to make sure they are within the normal ranges. It could take up to 10 miles of driving for an accurate LTFT reading.
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Note that it's normal for an engine to constantly alternate between running slightly rich to slightly lean air fuel ratio as it constantly adjusts around stoich 14.7:1