Over the past couple weeks, my 1996 Legacy 2.2 AWD wagon has started running rough, idling badly, hesitating on acceleration, and smelling like it's running rich. Initially, the check engine light came on, I had a guy scan it, came up with a code he said indicated loose fuel cap, took it off, put it back on, tightened it, cleared the code, and check engine light hasn't come back on yet. But the symptoms persist, and may be getting worse. The other thing: it's been getting harder and harder to fill the tank with gas, i.e. the pump wants to shut off before it's anywhere near full. So, I assume that the root of the problem is something fuel related, probably the evaporative system, but I'm puzzled by no check engine light. Also, I don't feel I really understand the evaporative system well enough to try to diagnose it. I stuck my head under the car and looked for OBVIOUS damage, like cracked or broken or missing hoses, major damage to the canister, etc. I didn't see anything wrong, but I didn't really know what to look for. The Haynes book is not very helpful, as it doesn't really explain how the evap system works and doesn't have good diagrams of the components involved. Can somebody help me understand better how it works (or is supposed to work) and how to go about finding the problem? Even just an illustration or detailed description of just what in the heck it is I'm looking at under there would be very helpful.

If you go to http://www.endwrench.com and click archives, then search for evap, you'll find some articles with descriptions, such as

 

Evaporative System Diagnosis

Evaporative Emissions Testing

[...]The other thing: it's been getting harder and harder to fill the tank with gas, i.e. the pump wants to shut off before it's anywhere near full. [...]

Here's another article that might help: http://endwrench.com/images/pdfs/VehicleWont.pdf