Left , inner fender well..says "MOT" on top
One larger vac line from engine manifold going into it, one coming out that goes to the emmissions canister.
It is fed a 12 PULSING sig when car is warm to get the gas fumes from the tank back into the engine for burning..if you place the valve in your hand, it will have a rapid beat to it [ closing/opening] about 6-7 htz.
It purges [ regenerates ]the fumes and does not do it in one gulp b/c if it did , it would effect fuel mix and give you your idle problems. So, a trick is to squirt the WD into the valve out port, let it sit for a while , and then run the engine ..that sucks the crap out of the valve and clears it up so it oscillates again..it is just an emmissions device , but when they stick open, they raise hell with the adaptations parameters of the a/f mixture.
So, I clean them , regardless , just cuz it is easy, cheap, known fault,... and doing so takes that possible out of the a/f mix equation.
Another test guys do when they have adaptation codes pop, is they just unplug the vac line to the purge and cap it..then run the car a few days and see if the adap gets back to norm..that verifies internal leak at purge..only problem w/that technique is you will bring on a purge code..but you know why, so you just clear it later..