Engine Performance problem
1998 Ford Escort 4 cyl Front Wheel Drive Automatic 211000 miles
After I have filled up the tank, the car runs fine until the gas gauge gets between the 1/2 and 3/4 marks and then it runs rough. Doesn't stall but has lower performance. I found that when I fill up it's fine so last night I opened the gas tank cover for a minute and now it runs fine.
Any ideas so I know what I'm looking at.