Anyone know what this part does?
I downloaded this and haven't read it in its entirety yet, so don't scold me if this is the wrong article.
Evaporative (EVAP) Emission Control Systems
Since gasoline vapors contain HC, these vapors must not be allowed to escape from the fuel tank to the atmosphere. In the EVAP system, a hose is connected from the top of the fuel tank through the tank pressure control valve (TPCV) to a charcoal canister. Gasoline vapors from the fuel tank are stored in the charcoal and then purged into the intake manifold when the engine is running under certain conditions.
A fresh air line is connected to the charcoal canister. Some EVAP systems have a fresh air intake directly on the bottom of the canister with a filter in the air intake. EVAP systems vary depending on the vehicle make and model year. Always obtain the exact system details from the vehicle manufacturer's service manual. A canister purge solenoid is connected in the purge hose from the canister to the intake port near the edge of the throttle. The PCM provides a ground for the canister purge solenoid winding to operate the solenoid.
How the system works
The PCM energizes the canister purge solenoid and allows vacuum to purge vapors from the canister under these conditions:
150 seconds have elapsed since the PCM entered closed loop.
Coolant temperature is above 176 degrees F. (80 degrees C.).
When the PCM is not enabling injector shut-off, such as on vehicles with traction control while one drive wheel is spinning.
The idle contact switch in the IAC motor is open.
Vehicle speed is above 20 mph.
Engine speed is above 1,100 rpm.
The engine metal temperature sensor is not indicating excessive temperature.
Low coolant level is not indicated.
If any of these conditions are not present, the PCM does not energize the canister purge solenoid, and the gasoline vapors from the fuel tank are stored in the canister.
When the engine is running, intake manifold vacuum is supplied to the TPCV valve. This vacuum opens the valve and allows vapors to flow through the valve into the canister. When the engine is not running, the TPCV valve closes, and fuel vapors are contained in the fuel tank. If the tank pressure exceeds 15 inches of water with the engine not running, this pressure forces the TPCV valve open and allows vapor flow to the canister.
The canister contains a liquid fuel trap that collects any liquid fuel entering the canister. Condensed fuel vapor forms liquid fuel. This liquid is returned from the canister to the tank when a vacuum is present in the tank. This liquid fuel trap prevents liquid fuel from contaminating the charcoal in the canister. The EVAP system reduces the escape of HC evaporative emissions from the gasoline tank to the atmosphere.
....It has now stayed on all morning on my drive in. 
