Chevy 4.8 idle issue and 420 code

hunterdan

hunterdan

Well-Known Member
Joined
Apr 13, 2009
Location
Morganton,NC
  • I have a 2003 chevy with the 4.8. Recently I got a 420 code(lean/low efficiency bank 1) I took it to local muffler shop and he of course says I need new cat.
  • I have read that it could be lean due to vacuum leak,intake leak,manifold before cat...and all these can throw the 420 code.
  • I can't find any vacuum leaks or leaks around exhaust/intake
  • Symptoms are cranks up immediately and runs at normal cold start RPM smoothly then when it drops down to warm idle it will stutter and eventually 2 miuntes later idle pretty smooth. I still have good power and fuel efficiency seems about normal.
  • I figure if I had a bad cat then it would be giving more signs like bad mpg,loss of power and such.

  • I have been having this code for about a month. First time I cleared the code along with a missfire code. 70 miles later it showed another 420 code. I then changed the inline fuel filter, cleared the code and went 800 miles and now code is back.
ANY IDEAS?
 
Intake gaskets, especially if you've never changed them. The cats on the 99-06 trucks rarely clog up from what I've seen.

The intake gaskets are a pretty simple job. A few hours one afternoon and you'd be good to go.
 
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