Thread: 420 code and rough accel.

i have a 05 gtp and about two days ago it started to accelerate really rough at about 3500 + rpms when i stepped on it the whole car will shake and accel very roughly i also have a 420 code
i am pretty experienced with this car but any input would help
thank you

i also gutted my cat thinking that it was clogged but that had no effect the problem
i am waiting on a new dp but would like to resolve this before it gets here

The code doesn't worry me but the shuddering and lack of power I'm getting is what bothers me acceleration is completely normal and I have no other problem unless I step on it

sorry about posting the same reply twice i was on my phone.
i checked all my fluids and none were contaminated and i dont have coolant in my exhaust.
but i did get the problem fixed today i got it rescanned and there was a new code for a misfire but the code for the catalyst is gone

im assuming since i got the 420 code my cat was going bad and it just took a little while for my misfire code to show up but i dont understand why the 420 code went away if i am running it catless

??????

the problem is fixed now i replaced the bad plug and wire im doing all of them next week sorry

i jsut had the exact same problem!!!! ac delco plugs 1 went bad and had to do them all last night what a pain the as$ the #6 plug is, wires are next!! put NGK 's in this time!