Q: Why does it do this??

All modern cars are equipped with an Evaporative Emission Control (EVAP) system. The EVAP system prevents fuel vapors from the fuel tank from escaping into the atmosphere. The EVAP system collects and temporarily stores the fuel vapors in the charcoal canister. The charcoal canister is filled with activated carbon pellets that can absorb the fuel vapors.

When the engine is running, the fuel vapors are purged from the canister and burned in the engine. The vent control valve (solenoid) controls the flow of outside air in and out of the charcoal canister. One side of the vent valve is connected to the charcoal canister and the other side is connected to the vent hose that has a filter or screen at the end and is attached to the car body or frame.

In some cars, the vent valve is attached to the canister; in others, it’s installed separately near the canister. The vent valve is controlled by the engine computer (PCM). Normally, the vent valve is open. It closes when the engine computer tests the EVAP system for leaks. If a leak in the EVAP system is detected, the Check Engine Light will illuminate on the dash and the trouble code related to the problem will be stored in the engine computer.

I would recommend having a professional take a look at your car to properly diagnose and replace your solenoid. If you have an air leak on the EVAP system, then the MAP sensor will not be able to determine the air density, and the MAF sensor will not be able to determine the volume of air entering the engine correctly. This will lead to over-fueling or under-fueling depending on the size of the air leak and engine operating speeds and load. Again, I suggest having an expert mechanic, such as one from Your Mechanic, take a look at your car to determine if the problem is with the solenoid or some other part of the EVAP system.