likely on the frame rail below or just behind drivers seat
top center of engine under/behind air filter housing
Try under drivers side on the chasis.
On my 1989 E350 motorhome, I had a weak fuel pump near the fuel filter. I replaced that and the problem went away. The pump in the tank was fine.
It's in the hood second from the front of the bus.
on the top of motor round black housing
might be a clogged fuel filter or some kind of leak in your fuel lines allowing air in the system.
your waste gate stuck open or closed , clogged fuel filter, dirty air cleaner dirty injectors
The fuel filter is mounted on a bracket affixed to the rear of the left-hand side motor/transaxle mount.
Have your tried replacing, and/or resetting your IAC valve?.
Electrical
Yes
It is important to know the fuel economy of a car while owning it. The fuel economy of a Ford E350 is 14 mpg city and 18 mpg highway.