Alright, I'm looking into this for a friend who has a 2.4 . Here's the story, she drove to work, was running fine, no problems. Ran inside and was back out to her car in about 5 minutes. Started it up and started to drive and found that the car was drastically underpowered, only going 30 MPH with it floored. She said the RPM's were also going crazy while she was flooring it. Her dad advised her to go as far as she could and about 200 years later the steering wheel locked up on her. She stoped for a while, started again, steering was fine but still had the drastic loss of power. It's a 99 (actually a grand am, but same car) with 66 thousand on it. If you guys have any ideas let me know because I'm at a loss here. I thought maybe a spark plug at first but i think it might be something more major because there would have to be more than one spark plug bad to only go 30, and for more than one spark plug to go at the same time at only 66k i dont think is very probable. Let me know.

any problem lights?
pretty much check everything you can, she may have killed her fuel pump, tho. who knows
if not, try this:
change fuel filter
run a bottle of seafoam in half a tank of gas

she didnt mention any problem lights, i assume she would have if she noticed any...............i somewhat ruled out the fuel pump because i've always understood it as something that either worked or didnt, no inbetween ........and with the whole steering locking and what not i assume it's a larger problem than a fuel filter and seafoam could fix, who knows

if there's no strange noises coming from the motor...

could be like 2fst4u said...

fuel filter, check the plugs, change them if necessary, check wiring, check oil, check coolant, check air filter, check for spark on all 4cyl...

after that and the diagnostic shows nothing, fuel pump, injectors are they firing? are all grounds in place? how well was the car taken care of?

yeah definatley check the injectors, try using a bottle of lucas fuel injector cleaner.....

thats a crazy story....

Almost the exact same thing happened to one of our vans at work. It ended up being the fuel filter that was clogged with sand...and a lot of it. How that much sand mysteriously found its way into the gas tank is beyond me but they dropped the tank, cleaned it out, and changed the filter and it ran perfect again. Have your friend get the fuel filter checked as well as the tank.

fuel filters are cheap too, i would just change it anyways