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2000 Silverado misfire at idle HELP!!

Discussion in 'General Chevy & GM Tech Questions' started by dc9689, Apr 10, 2010.

  1. dc9689

    dc9689 New Member

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    Hey guys I just had a new engine put in my 2000 Silverado. Its another 5.3 out of a 2000 silverado everythings the same. The truck seemed to run fine but now im getting a p0300 code and when my buddy hooks up his computer to the truck its misfireing on cylinders 2 and 7 but only at idle, when you get on it it goes away. Weve swaped out plugs, made sure they were gapped correctly, new wires, switched the coil packs out, and switched the injectors. And it is still misfireing on 2 and 7. If anyone has any info or suggestions it would be greatly appreciated, im lost! Thanks guys
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  2. murdog94

    murdog94 New Member

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    IAC??? Might need to be cleaned. Did all the pins in the harnesses stay put or mabey there are a couple pulled through... Throttle position sensor?? Just a few things than can cause this.. im sure some other people will chime in with other possibilities.
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  3. fishinrebel83

    fishinrebel83 New Member

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    idle issues

    hey man,
    i had the same issue with my truck, same year everything, i let it go a little to long and then i started thaving issues with it starting, i had to pump and hold the gas to get it started, found out it was a 35 dollar fuel sensor swith its located behind the alternator, its a little black cap looking peice. i got that changed and never had another issue with that truck. i know it sounds really weird but thats what the issue was when i had the same problem.

    hope i was some help
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  4. dc9689

    dc9689 New Member

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    whats the iac? and ill have to check that sensor out! Thanks alot.
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  5. nos351wcm

    nos351wcm New Member

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    the IAC is the idle air control sensor. it is mounted on the throttle body housing. If you switched coils plugs and injectors, and still got mis-fires on the same cylinders, then the problem lies before the coils, what i mean by this is the problem could be a bad connection between the ECU and coil or injector. it could be a ground not hooked up, or like someone said one of the pins in the harness got pushed through.
    hope this helps
    #5
  6. dc9689

    dc9689 New Member

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    Thanks for your help guys, ill have to keep trying tomarrow!
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  7. murdog94

    murdog94 New Member

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    Agreed, but sometimes the computer will also throw those codes for a faulty IAC.. Ive seen this happen both ways..
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  8. dc9689

    dc9689 New Member

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    hey guys well i thought the problem was solved but i was wrong. I checked the plugs there gapped corectly and the wires are in great condition. I changed out the iac and the problem seemed to go away, but after drving for awhile the ses light came back. The ses light will come on and then awhile later go off. Im lost now for what elese to do. DOes anyone have ideas? Also i cant find that fuel sensor behind the alternator? Thanks again i appreciate the help!
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  9. dc9689

    dc9689 New Member

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    Anybody???
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  10. 2COR517

    2COR517 New Member

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    What are your plug gaps? Should be .040
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  11. dc9689

    dc9689 New Member

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    yes the plugs are all gapped to .40. I dont get it the truck runs great no with no problems, and the ses light will come on for awhile and then it goes back off and then repeats later on.
    #11
  12. shadetreemech

    shadetreemech New Member

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    SOME of the misfire related codes that I have ran into is the Fuel Pressure Regulator goes south giving you a lean / rich curveball to the computer , fire up the truck and pull the vac line off the reg. you should not see any fuel seeping or running out. Hope this helps
    #12

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