My 2003 jeep liberty wont start without keeping foot on gas. Had to drive 2 miles home without taking foot off gas luckily made all the lights

that lamp says SCAN me now.
why not do that. its talking, all you need to do i s listen.
can be 50 things. why guess.
step one, scan it.
buy a tool, rent one, barrow one, or get car scanned by any ASE Tech. google find and ASE shop near me. bingo. the best.
btw , it might only need a tuneup
ever do one in 10 years? those parts never last 10 years.... so.....
that is why it is done.

Make sure that one of the brakes have not locked up not causing it not to move.

it does sound like a broken trans or maybe even a rear differential

have the fault codes read as that will indicate the problem area

Assuming everything is working correctly, you may have to drive it up to 50 miles for the computer to relearn the basic perimeters.
I think you can also turn the key on, open the throttle to wide open, then close it 2 or 3 times to reset the memory in the computer.
Not sure about Jeeps.

Did this happen overnight or was it a gradual loss? Did you do any kind of repair before you lost the gas mialage? Is there a check engine light on or did it come on and go off? Did anything weird happen before the jeep got bad gas mileage? It's hard to diagnose a problem like this without actually touching the car.
Any other info might help me steer you in the right direction.

when was the last time you put in fuel injector cleaner? I put in Lucas Oil Injector cleaner every other or every oil change.

There are alot of factors affecting your gas mileage. Tire wear, tire pressure, wheel alignment, air filter, fuel filter, spark plugs, oxygen sensors, just to name a few. So to say what you need is just shooting in the dark without more information. I would probably start with your oxygen sensors, and then perform a tuneup. If your vehicle pulls to one side or the other when driving on the highway you need to stop into the shop for a wheel alignment.

If your engine light came on, the engine module could have stored a code.
You need to have a scanner to check what code it is and that will point you toward the solution.
Possible causes could be (crank sensor, tps sensor or oxygen sensor).
Don't go replacing parts until you scan the vehicle for codes first.

YOUR BATTERY HAS LOW VOLTAGE, NOT ENOUGH TO KEEP IDLE CONTROL VALVE OPERATIONAL. REPLACE BATTERY AND YOU'LL SE THE PROBLEM GONE.

My jeep when empty still has 6 gallons approx left with the light on, i assume the sending unit took a ****, or the float is messed up. As the 2 people above i would say the method to fix your problems is having the sending unit replaced. Which means taking the fuel tank down and replacing the sending unit which housed the fuel pump and the float/line. Not cheap.