Newbie here with a cel question

I have a 2001 4 door trd Tacoma with 3.4 motor and 4wd. It runs good and the cel (check engine light) stays off until I am decelerating from highway speeds. When it pops on it runs rough. The engine will not rev over 2000 rpm. Weirdest thing.
Few notes
I have a k&n filter and I regularly clean the maf.
Can't remember the code. I think it's p0420 if I remember right.

Does anyone have any suggestions.
Will the urd o2 sim help me?

 

Fouled out spark plug?

 

I have recently changed them. Plus it runs fine most of the time.

 

Seems like its going into limp mode which is the computer protecting the motor from its full potential to prevent damage. That's the purpose of your revving issue. As for the CEL code it is a generic code that all OBD II cars have when their is an issue. The code is the catalyst system efficiency is below threshold. Meaning your catalytic converter is throwing the code. Could be your O2 sensors going out. There are two sensors (I THINK) so you will have to figure out which one it is. It is also affecting you fuel mileage so I would get it fixed asap, not hard to do yourself but get the right tool because those sensors are hard to take off due to the heat from the exhaust.

Hope this helps.

 

Has anyone had experience with the urd o2 simulator?

 

So I just got back from autozone and the code that it's throwing is p0120. Throttle position sensor.
This is defiantly a new code. Usually it throws p0420

 

Is this problem usually solved with a new throttle position sensor?

 

Typically the sensor talks to the computer however when the communication stops it throws a light on your dash. Sometimes the sensor will begin talking with the computer again and doesn't need to be replaced but this is a sign that the sensor is nearing the end of its life. If the dash is always having the light on then the sensor will need to be replaced. Sometimes you can delete the code and wait to see if the light comes back on.

 

Decided to just replace the sensor. I need to stop being a tight ass

 

ha