Check engine light. trying to diagnose.

[Zashra]

So my 03' GT-S has the check engine light on. we got it scanned at and auto zone and the computer said it was an Oxygen sensor or the catalytic converter. so im trying to confirm what it is.

Symptoms: significantly decreased horsepower/torque. poor gas mileage.

Things i've tried: Cleaned the MAF sensor.

So does anyone know what migh cause the symptoms? is it the O2 sensor?

-Thanks

[Zashra]

Forgot to mention. it also does not rev properly (primarily why the horsepower is low.)

Basically it will rev all the way to the limiter in any gear as fast as it does in first. when i step on the gas in 6th the rev will just simply climb and i get very little benefit from it. this makes acceleration rather difficult as my car struggles to build up the torque required to move. i have to floor it spiking the revs up around the 5500 - 7000 range, in order to accelerate at any reasonable rate.

[mrlieu]

Probably the o2, changed mine with 150,000 miles on it and the car felt it had more power through the rev range/ better fuel economy too.

[Zashra]

ok. yeah mine has 140k miles and i don't think much has been replaced from the first owner. whoever had this car prior to me took so-so care of it. lots of weird stuff. for example the plastic sheet inside the door panel is cut open on the driver's side.

[Jasonhughes2009]

plastic in the door panel was cut most likely to replace a window motor or lock actuator. could be o2 not switching correctly or it could be biased.

could be partially clogged cat as well. which o2 sensor code was it.

[Jasonhughes2009]

also could be a different problem, clogged injectors, fuel pump crapping out on you, causing the o2 code to go on because its always reading lean and no torque due to low injector flow