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Thread: 2003 Tahoe with post warm up rough idle

  1. #1
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    2003 Tahoe with post warm up rough idle

    Guys this is getting frustrating. I have a 2003 Tahoe 5.3 flex fuel that started off throwing a code for MAF 10 weeks ago. I cleaned the MAF and reset the code without issue. One month later light came on and the code was for lean left and lean right. At this time it began to idle very rough a couple minutes after start up. Five to ten minutes of run time and the rough idle would go away. Mechanic changed fuel filter prior to a trip I was making. The next day the light came back on. I changed the forward O2 sensors in an Autozone parking lot and still no relief. Next I changed the plugs and wires. No help. The codes had now expanded to include random misfire and possible purge valve solenoid. I changed the purge valve solenoid and MAF and reset. Today at start up it still idled very rough a couple minutes after start up. I drove it and the light came back on. Checked and the codes were for lean left and lean right. Right back where I started. It was noted today that the idle was at 540 rpm.

    At this point it seems that the problem is a low idle. At start up it runs fine. After a couple minutes it runs rough. After it warms up more, it runs fine. If I hold the rpm up during the rough idle, it runs fine.

    Today it was recommended that I look at the catalytic converters and vacuum lines. I am feeling a little lost. I read on an old post that these symptoms could be due to a leaking intake, clogged EGR valve, dirty throttle body or bad idle air control valve.

    Thanks in advance for any help.

  2. #2
    Senior Moderator chevychase's Avatar
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    Random misfire ... lean bank 1 lean bank 2 hard to diagnose these. 03 would not think cat. Seems if it was a vac leak would idle a little fast.
    What type of air filter? Will think on this .

  3. #3
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    Just running a Fram filter. It seems crazy that it runs so perfect after that initial warm up period.

  4. #4
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    It does have 127k on it.

  5. #5
    Senior Moderator chevychase's Avatar
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    Do this make sure all is tight down stream of maf... any air leak will create probs.
    Have you changed fuel filter... check fuel pressure at least 58 psi and hold.
    Lean condition air fuel ratio off more air than fuel. Go ahead and check for vacuum leaks ... will not get any better response from a certified mech.
    Theses are hard to diagnose. Could have a live scan done on it.

  6. #6
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    Fuel filter has been changed. I will check for air leaks down stream, the fuel pressure and for vacuum leaks next. Thanks for the help. I have done a lot of change and hope so far.

  7. #7
    Senior Moderator chevychase's Avatar
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    More i think about it intake gasket maybe leaking... will do this on start up.. then when engine gets warm will close off some.
    Due to heat expansion.

  8. #8
    Senior Member repairman54's Avatar
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    Engine temp sensor may be off at the lower temps and close enough after it warms up.
    My sisters Malibu eats them......
    ______________

    John
    '99 Yukon
    FLHR
    Doo 1200 GSX

  9. #9
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    I see........

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