[chasealley]

The hiss you hear in the driver's side fender is normal and not related to your poor running problem. I believe all Windstars of that vintage have it. Mine does and I used a stethescope toi find it. I was able to peek inside the fender and see that the intake for the air breather jst terminates inside the fender. That's right. It goes into the fender and all that is there is a piece of flanged tubing. The proximity to the driver and the placement in the empty cavity make it a poor design from a sound standpoint.

Anyway, the hiss is nothing to worry about as far as I know. It gets louder when the engine is under load like when I turn the steering wheel or immediately after starting and then goes away. Try turning your steering wheel for fun and see if you have the same noise. Some do, some don't.