420 code and rough accel.

[theshznt69]

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

[theshznt69]

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

[gtpinsc]

a gutted cat will still cause p0420... ive been running with that code for months due to not having a cat and it never caused any other issues other than ses light.

[theshznt69]

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

[gtpinsc]

sounds like maybe its misfiring? check wires, plugs, coil packs.

[theshznt69]

ignore this

[gtpinsc]

sounds like maybe its misfiring? check wires, plugs, coil packs.

this or is your LIM leaking?

[theshznt69]

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

[gtpinsc]

so what was the problem?

[theshznt69]

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

[gtpinsc]

......

[theshznt69]

??????

[theshznt69]

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

[reallyfast1]

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!