Hello all, I am a new member and not very versed at how to use forums. I was hoping that someone might offer suggestions on a problem I am having with my 2000 Deville. After some rough idling from the car and a check engine light and a P0420 code, I installed a new catalytic converter and reset code and it seems to have done the trick and the code didn't return. However, after a few days, I am getting a rough idle from time to time, not always. When I get the rough idle, I can take it out on the road and 'blow it out' real good and it starts idling normally for a few days or so. There are no codes except for IPM B0429 - Temperature Control #3 Rear Circuit Range/Performance. Can anyone offer suggestions as to what I could try to fix the rough idle? I would appreciate any advice very much.
Thank you,
Greg Mitchem

 

p0420 usually a cat
but there must be something else happening.
have you cleaned the throttle body nad the air filter is clean and good?
do you use one gas station or many different ones??
when u get a rough idle is there a flash service soon engine light?
do u notice alot of black carbon built up on the tail pipe?
do you smell gas?

 

Thank you for replying to my post, I have been out of town a few days and was happy to see that I had gotten a reply when I returned.
I will clean the throttle body and change air filter, we do normally use a few different gas stations, but since the rough idle is not everyday, I wonder if it could be attributed to one gas station over the others. I will try to change gas stations, do you have any suggestions on any gas better than others. I have gotten a flashing service soon engine light a few times when the idling was rough, but it went out as soon as the car was driving down the road and not stopped. I haven't noticed any carbon build up on the tail pipe and haven't smelled any gas. Do you know what the 'flashing' engine service soon light could be about? Once again thank you for replying and any further advice would be greatly appreciated.

 

I'm back again. Now the service engine light is on the code is: P0300 multiple misfires and still idling rough in and out. Where do you think I should start? I hope you have some ideas, for me. Thanks

 

I would start by checking coils. If coils are ok and the problem goes away while driving it sometimes i think you have some bad ignition wires

 

u have a misfire happening at idle
it may be there when driving away just not as noticeable.
a flashing light means emisson control
misfire-- spark plug or wire
bad injector

fuel
carbon build up
you need to get a scanner hooked up
you will be able to see which cylinder is misfiring or you should be able to go to the on vehicle computer it should say

p0300 general misfire
p0301 cylinder 1
p0302 cyl 2
etc
after u pin it down
to check wire just change with wire beside it
if misfire moves to that cylinder its a wire

do the same with the spark until u elimate all options
easier with a scanner but this way will work to

you do however have to erase the codes
it should reset quick due to it is flash

 

Thanks guys, I will give it a try.