'04 Silverado, 4.8L, rough idle, no codes set ?

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by 04-silverado, May 14, 2010.

  1. 04-silverado

    04-silverado Rockstar 100 Posts

    hi all, need some help

    (new here, but not new to basic maintenance of vehicles... I'll be 60-yrs old next month)

    Purchased a 2004 Chevy Silverado 1500 (reg. cab, 8 foot bed, 4.8L, no frills), with 97,400 miles on it, on the 5th of this month. Today (May 14th) I did the following:

    * Cleaned MAF Sensor and Throttle Body.

    * Replaced all Spark Plugs with Autolite Double Platinum copper-core APP5245s (they came gapped at 0.055). I regapped them to be 0.040 (the old ones were APP5245, gapped as indicated below). All of the old plugs were NOT tightened/torqued as they should have been... and #1, #3, and #6 were less than finger-tight!

    1 - 0.063
    2 - 0.065
    3 - 0.067
    4 - 0.065
    5 - 0.064
    6 - 0.063
    7 - 0.067
    8 - 0.064

    All of the plug wires looked to be in good condition, and they read between 910 ohms and 945 ohms of resistance... so I left them on the truck. I reinstalled everything using a bit of anti-seize on the plug threads and dielectric grease on the plug boots.

    A bit of a rough idle (no codes set) and noticeable hesitation were the reason for my under-takings as noted above. After completing the above... there is no hesitation and the idle is almost smooth (way better than it was before I started).

    With no codes set, and no CEL indications, I presume I should just drive it for a bit to see if the idle will completely smooth out. On FORD products I have owned & worked-on, one could disconnect the battery... short the POS and NEG battery cables (NOT the battery terminals!) together, for about five minutes. This would completely RESET the computer, and once power was hooked-up again... the first 10-miles / 10-minutes or so of driving would allow the computer to "relearn and optimize" the system.


    I'm curious if CHEVY has an "adaptive" computer (anything like the FORDs)?

    Is there anything else I should look at (given "no codes set") and a not "perfectly smooth idle"?

    TIA - karl
  2. 04-silverado

    04-silverado Rockstar 100 Posts

    Ok -- I've driven it for a few days now without doing anything further to it. It seems to be running just fine (perhaps I was just being overly sensitive to any variations in the "idle"?). But the original "rough idle" and "hesitation" have caused me to be a believer in the saying "trust no one"!

    This vehicle was serviced by a FORD dealer in DE, apparently not long before it was bought at auction (by the used car dealer, in Southeastern VA, from who I bought it). It started just fine... and while warming-up the idle seemed fine (I suppose), but as the engine reached operating temperature that's when the "rough idle" became more noticeable (while sitting at stop lights, for example).

    One thing is for sure... whomever changed the plugs did NOT gap them properly, neither did they torque them properly. IOW: "trust no one" (do it yourself, if you are capable)!
  3. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    Agreed, also have you tried the seafoam trick since your near 100K that might help to clean things out further.
  4. 04-silverado

    04-silverado Rockstar 100 Posts

    Thanks for the feedback!

    When I first noticed the "rough idle" I did clean both the MAF sensor and the Throttle body:

    I cleaned the MAF Sensor using CRC Mass Air Flow Sensor Cleaner and the Throttle Body using Sea Foam Spray. I've not used any other products for those chores, but I am open to suggestions. :glasses:

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