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2003 Chevy 3500 6.0 rough idle and rattle? P0300 DTC Any Ideas?

This is a discussion on 2003 Chevy 3500 6.0 rough idle and rattle? P0300 DTC Any Ideas? within the Technical / Maintenance forums, part of the General Discussion category; Hey Guys, I have a 2003 Chevy 3500HD 6.0 with an automatic trans, it has 40,000 miles and is in ...

  1. #1
    Registered User Leviticus's Avatar
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    Angry 2003 Chevy 3500 6.0 rough idle and rattle? P0300 DTC Any Ideas?


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    Hey Guys,

    I have a 2003 Chevy 3500HD 6.0 with an automatic trans, it has 40,000 miles and is in cherry condition.

    Ok so it started running rough at idle and would sometimes get that stab misfire when in D at a stop and would sometimes hesitate when taking off from a stop and feel like it was going to die. Its popping the P0300 over and over and just idles weird, the exhaust has that boom boom boom instead of the normal V8 sound and it has a rattle in the engine when at about 1300 RPM's in park and only when coasting at the same RPM but no under load. It seems to run great under load in the upper rpm's but idles crappy. Since relacing all the below items it doesn't pop the P0300 anymore but still idles and runs weird. I an going in on Monday since the emmisions, cats and injectors are still under warranty. Any Ideas???

    So far I have done:

    New plug wires

    Checked the plugs and all were lightly browned dry and clean all worn evenly

    New PCV valve

    Cleaned MAF

    New air filter

    Fresh Synthetic Oil and Filter service

    New fuel filter

    Checked fuel pressure 59 with engine off and key on and 52-54 running

    no gas in fuel FPR vent hose

    oil pressure about 40 idle and about 50 running 2200rpm on the freeway and while in the throttle.

    cleaned ground for ECM

    re torqued upper intake manifold mounting bolts

    sprayed carb cleaner around intake ports with no change in idle

    cleaned throttle body

    Help!!!

  2. #2
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    Re: 2003 Chevy 3500 6.0 rough idle and rattle? P0300 DTC Any Ideas?

    Quote Originally Posted by Leviticus
    Hey Guys,

    I have a 2003 Chevy 3500HD 6.0 with an automatic trans, it has 40,000 miles and is in cherry condition.

    Ok so it started running rough at idle and would sometimes get that stab misfire when in D at a stop and would sometimes hesitate when taking off from a stop and feel like it was going to die. Its popping the P0300 over and over and just idles weird, the exhaust has that boom boom boom instead of the normal V8 sound and it has a rattle in the engine when at about 1300 RPM's in park and only when coasting at the same RPM but no under load. It seems to run great under load in the upper rpm's but idles crappy. Since relacing all the below items it doesn't pop the P0300 anymore but still idles and runs weird. I an going in on Monday since the emmisions, cats and injectors are still under warranty. Any Ideas???

    So far I have done:

    New plug wires

    Checked the plugs and all were lightly browned dry and clean all worn evenly

    New PCV valve

    Cleaned MAF

    New air filter

    Fresh Synthetic Oil and Filter service

    New fuel filter

    Checked fuel pressure 59 with engine off and key on and 52-54 running

    no gas in fuel FPR vent hose

    oil pressure about 40 idle and about 50 running 2200rpm on the freeway and while in the throttle.

    cleaned ground for ECM

    re torqued upper intake manifold mounting bolts

    sprayed carb cleaner around intake ports with no change in idle

    cleaned throttle body

    Help!!!
    Sounds like you have narrowed down quite a few things. Is your new air filter, or old air filter a k and n?

    For what its worth, we had the exact same problem with our 6.0 at about 85k. Cleaned the MAF with Electrical cleaner, carb cleaner, and even MAF cleaner, none helped. I replaced the MAF with just an ebay unit and it runs great now. Just throwing that out there...
    ThankYouSoldiers

  3. #3
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    SYRACUSE NY & ALEXANDRIA BAY NY
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    Re: 2003 Chevy 3500 6.0 rough idle and rattle? P0300 DTC Any Ideas?

    Is it stock? Mods if any?

  4. #4
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    Re: 2003 Chevy 3500 6.0 rough idle and rattle? P0300 DTC Any Ideas?

    Well, (obviously) you have a misfire. It really sounds like an vacuum leak to me, but you covered that decently I think. It could be an injector though. I think the first thing would be to try and see what or which cylinder(s) are missing. The method I would use would be to pull injector wires off and see which one doesn't change the idle (unless you have a scanner with misfire counters). Then maybe sway injectors with a different cylinder and see if the miss follows.

  5. #5
    Registered User Leviticus's Avatar
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    Re: 2003 Chevy 3500 6.0 rough idle and rattle? P0300 DTC Any Ideas?

    Hey,

    No its all stock, I used K&N's on my Chrysler crossfire and my Land Rover disco and it screwed the MAF on the Rover but they work great on the Crossfire. I Just have a new STP paper filter in it.

    Yea it might be the MAF, it would explain why it wouldn't narrow it down to one cylinder due to excessive or lack of air it would affect all of them thus the P0300 code. It sat barely driven on my ranch for the last couple of years maybe 3-4000 miles but it has gone through at least 30-40 gallons of gas and I used a bottle of Lucas Cleaner in both tanks.

    Keep the ideas coming and how much did the MAF run you $?

    Thanks Guys !!!!

  6. #6
    Registered User
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    Re: 2003 Chevy 3500 6.0 rough idle and rattle? P0300 DTC Any Ideas?

    I went cheap and bought an ebay unit for like 60 bucks. I think it had a ding on the screen, runs great though. They can be had all day long from 100-150 though.
    ThankYouSoldiers

  7. #7
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    Re: 2003 Chevy 3500 6.0 rough idle and rattle? P0300 DTC Any Ideas?

    Have you thought about the intake gasket? Mine sets the same code and that's what I have it narrowed down to, just haven't done it yet.

  8. #8
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    Re: 2003 Chevy 3500 6.0 rough idle and rattle? P0300 DTC Any Ideas?

    MAF sensors will usually throw rich or lean codes before they throw a p0300.

    might be an injector spray issue. since youve got a miss at idle( right?), you can drop cylinders until you find your weak hole. or you can take a temp gun, if youve got one and check the exhaust. the cool one is your miss.
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