Sudden acceleration both while stopped or while driving and check engine light always on

the ECU shuts down all cars (cruise controls) if ECM or TCM sees hard errors, for safety and by law. even brake lamps dead. and more.
never put additives in the gas tank ever, for sure Marvel mystery Oil ever or wreck the injectors you will, a horrible act.
lost power is normal on overheating engines. (cause and effect)
the engine needs service, like 99% of all 26 year old cars.
It will; have lots of problems is not serviced regularly.
USA car?
back in 1996 ECU only some simple checks by ECU then OBD2 USA./
it is just basics not a very smart, Check engine light*(CEL)
In Canada, the ECU is even more DDummbb(sic) this year.

check oil levels at every fuel fill up, on 26 year old engines.( for sure)
that old the joke is
"stop at the Station,and fill up oil, and after check fuel too if needed."

do not drive cars based on dash lamps, do the checks your self
even look for coolant leaks hood up hot engine,
check for belts frayed or loose or missing
check for brake fluid leaks, all corners and master cylinder , levels good.
make sure you run 50% Antifreeze for engine coolant, fresh is best.
not pure water, ever, or it will boil over , for sure.

yes it needs service, nobody here can look under the hood and test things, using real tools. (in a text box) but can say get it serviced.
with real coolant. the boil point is 265F, so if you ever hear or see it boil, you now that is a hard failure and to not drive it but stop and fix it. or damage can go worse warping head or block or worse.
at this ages, most hoses here are totally EOL , end of life)
and the thermostat too.(or more)

run the fault codes
could be a broken timing belt or chain
could have blown the main power fuse next to the battery ( around 80 amps ) and that would have switched everything off

How old is your vehicle....most common problem is throttle position sensor...

Always check for trouble codes when the check engine light turns on during engine running. After repairs are made, a scanner can be used to erase the codes.

It sounds like a fuel problem, so you would need to have the fuel pressure tested. This will verify the fuel pump and fuel filter are not the problem if the pressure is correct.

check if the fuel filter needs replacing

oil, check engine and battery will always be on when the engine is dead--because there's no oil pressure, nor battery charging. A faulty oil pressure sending would never prevent the engine from starting. You'll have to tow it to a shop to find out why

The DAMN THING has 200,000 MILES on it, give it a break, it is just waring out, drive it easy. (most likely burned valve)

when you press the gas can you hear the engine accelerate if you can then that means it is your transmission if you cant it is your gas cable linkage just snap you can just replace it by removing your engine cover then add a small nut and tie it to the end of your gas linkage strech it in to the plastic arm and you can then use it to take to your mechanic to fix it properly

ASE Mechanic here:
Check engine for good tune up, may those spark plugs are fouled out beyond belief, its always best when changing motors to use known good parts....