CEL after Coils/Plugs/02 Sensors were changed...

[Bluenote]

Guys,

I have a 2005 Lincoln LS Sport with 88K mi.
As the subject states I recently changed "All" Coils and Plugs to fix an ETC Fail Safe Mode reading and 2 weeks later I changed "ALL 4" 02 Sensors after getting a CEL-Code of P0420. I disconnected the Battery to reset the CEL; drove the car approx 45mi and the CEL light came on again. I took it to Pepboys to diagnose the Code and there was No Code (The guy reset the CEL light and it was off.) On Christmas I drove the car approx 140 miles and 10 min. before I get back home the CEL is back on...The car ran fine, very smooth no problems that I can detect. Are there any other areas that could contribute to a CEL after changing all these components?

Suggestions are much appreciated.

 

[dNyce LS]

That code is catalyst below threshold (iirc). Misfires tend to f up the cats

 

[Bluenote]

Yeah, I was hoping that Mis-Fires were addressed with the Coil/Plug replacement. Is there a way to determine a non-apparent mis-fire?

 

[Bluenote]

I hope it's not a CAT Converter replacement. Those things are extra expensive in Calif...

 

[dNyce LS]

idk for sure, someone else may know.
but, i do know that the car rumbles some while at idle (usually more if its in gear, less in park or nuetral). most times it wont throw a code though