93 f150 check engine problem and fuel tank.

First, the check engine light is on and it
turn on in the first 3 seconds after I turn on
the truck. When that comes on, I have to
keep my feet on the gas and brakes at the
same time so that it won't stall out. If I put
it in park the RPM will get low but won't
cut of most of the time. I'm not sure what
to do. I did just changed the spark plugs.
Second part is the gas tanks. I have the
dual gas tank and the rear tank started
leaking gas so I started use the front tank. I
would fill up the front tank and drive it
somewhere and it would be fine. If I turn off
the truck and wait like 10 or more mins
than I would come back and 1/4 of the gas
would be gone but just before I got out it
said it was full and I didn't drive no more
than 10-15 mins. Like today I filled up the
front tank and drove 45 mins to school and
I was there for like 7 hours. When I started
my truck it says it was empty. There was
no gas on the ground or I didn't smell it.
When I got on the highway and was doing
like 75 mph it went up to half a tank than
when I got back home it says it is empty
and it a little over the red line. If u know
what's wrong with either question than can
u let me know