Almost all cars after the 90's have a MAF sensor. The MAF sensor detects airflow thereby sending signals to the engine to adjust how much fuel to deliver. They oftentimes get dirty from years of driving, and the sensor gets clogged with dirt and oil causing poor gas mileage as well as poor performance. Your car may even throw a Check Engine Light (CEL). In my opinion, most MAF sensors don't need to be replaced, but just a good cleaning will make the MAF sensor perform like new again.
Disclaimer: This is for demonstration purposes only. Removing and mishandling the MAF Sensor can be a costly mistake. Some of these newer sensors go for a few $100. Proceed at your own risk.
Materials:
CRC/Mass air flow sensor cleaner
Flashlight
Q-Tip
Tutorial:
1. With the car off and key removed, disconnect and remove your MAF Sensor
3. If the gunk is still stuck on the wires, grab your Q-tip and spray some MAF cleaner on it and again down the hole. Carefully clean and rub the wires as they are very fragile. If you break the wire, then you'll need a new sensor.