I'll make this as brief as possible...I parked my 91 Fleetwood at my parents house 2 weeks ago. I disconnected the battery on the positive terminal. Today I connected the terminal and started it up. It ran fine...I backed it out of the driveway and shut it off. 2 minutes later I started it up and it ran like sh*t. Figuering it needed to be taken for a ride I got in and it barely made it up the hill. Once driving it for 20 minutes it runs o.k but not good....seems like it's starved for fuel. The car bucks and does not want to accelerate at all. When coming to a stop it seems like the trans is not down shifting in sync with the motor. The "check engine" light comes on steady than shuts off if I let the car idle for about 5 minutes in park. This would continue all night long. The car runs terrible and doesn't want to start once I shut it off (even if it's for 1 minute).

Keep in mind this car ran excellent before I parked it.
BTW the car is a 91 Fleetwood with the 5.7 motor and 58,000 miles.

The only things that I've been thinking are....
1. Did I short something out by disconneting the battery?
2. Did someone put something in the fuel?
3. Could it be something simple like a fuel filter?

Not that I am an expert I have to say you should have unplugged the negavtive battery cable instead .As I recall, this is a correct way .Still, I don't think by doing this you damaged the car's electrical systems unless you see some smoke,fume when re connecting the cable .
Your symptoms seem to me a misfire condition .It might be one of plugs or plug wires as well besides fuel filter

Fuel pump?

Do you hear it power up when you turn the key once?

Fuel pump?

Do you hear it power up when you turn the key once?

Wasn't paying attention, but I'll check today. Would that trip the "check engine" light?

Nope, fuel pump would not show a CEL.

May I ask why you disconnected the + for two weeks? Do you have any enemies? Could be fuel issues. Try the whole process over removing both + & - for at least 30 minutes. Also check the air intake from inlet back. A few years back I had a bunch of leaves clogged in my maf,it crippled the car ,and left me stranded on the roadside.

May I ask why you disconnected the + for two weeks? Do you have any enemies? Could be fuel issues. Try the whole process over removing both + & - for at least 30 minutes. Also check the air intake from inlet back. A few years back I had a bunch of leaves clogged in my maf,it crippled the car ,and left me stranded on the roadside.

Haha...Yeah. Around my parents house these old Cadillacs get stolen and stripped. With me not around, I figure I can stall them long enough for my father to shoot em. Back to the issue though...I'm gonna try that today and let you know.

If this happened to me I would immediately starting poking around the ignition system. Even though it may seem unlikely, check for spark at all the plugs, check wires and contacts for corrosion, after that starting checking distributor and other ignition timing components.

Weird thought, but might you have a MOUSE NEST somewhere in the intake system?
This time of year in New England it is a real problem with small critters making homes in cozy places that seem safe from predators like cats and intake plenums are just peachy for mice.
Thus, when you fire things up, the mice and their nests get sucked up into where they clog things very nicely.
This has happened to at least three friends with classic cars which are not driven on a daily basis.

Weird thought, but might you have a MOUSE NEST somewhere in the intake system?
This time of year in New England it is a real problem with small critters making homes in cozy places that seem safe from predators like cats and intake plenums are just peachy for mice.
Thus, when you fire things up, the mice and their nests get sucked up into where they clog things very nicely.
This has happened to at least three friends with classic cars which are not driven on a daily basis.

Not a bad idea....I'll check it out this weekend.