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Thunderbolt's avatar
Thunderbolt
Explorer
Feb 07, 2018

Rough Idle

I have a new issue will my 03 Chevy 6.0. When the truck is cold it idles rough. Doesn't actually feel like a misfiring cylinder. In gear at a stop light the idle will drop below 500 rpm and the engine stumbles and then the idle jumps up to about 1,000 rpm and then back to normal for a moment and then it repeats. Once it was up to operating temp it idled fine. Since it only did it when cold most of my research showed tat the intake manifold gasket was the likey the problem.
Now this morning the temp outide was -6 degrees and the truck ran rough until it was warm and then it was fine as usually. Then 25 miles down the road I run into traffic and had to stop and the truck did the same rough idle as it was doing when it was cold. It did it about 5 or 6 times and then idled fine again. Warm or cold it runs fine once you are off of idle. Looking for some input.
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  • kw_00's avatar
    kw_00
    Explorer
    Feb 07, 2018
    I had my old one do the same. Intake manifold gaskets were leaking. After I fixed that issue I had the Cpk go out.... that was a easy fix as well! That 6.0 is so built proof that I bought an 09.. my old one had over 200k. So that's my take on it, replace the gaskets with the newer updated ones. Good luck and keep us posted.
  • Jay_Pat's avatar
    Jay_Pat
    Explorer
    Feb 07, 2018
    From what I've read, it could be sticktion(?)with one of the injectors.
    Arches diesel treatment has been known to eliminate sticktion.
    If you can't find it on the shelf at auto parts, I would try any diesel treatment.
    Pat
  • Thunderbolt's avatar
    Thunderbolt
    Explorer
    Feb 07, 2018
    LIKE2BUILD wrote:
    Remove the idle air control valve and thoroughly clean it and the cavity. A sticky valve with respond to the ECM properly but not physically move. So, you can get odd idle behavior like you saw but never trip a check engine light.

    My FIL had a chevy van that was racing at idle. He could go 45MPH and never press the throttle and had no check engine lights. I replaced the AIC and all was good.

    KJ


    I don't think the 03 and newer actually have an removable IAC like the older ones did.
  • NJRVer's avatar
    NJRVer
    Explorer
    Feb 07, 2018
    I received a letter from GM on my '09 6.0 about rough idle quite a few years ago.
    If my mileage was still under 100,000 and the rough idle happened the letter said to bring it to the dealer.
    Of course I had over 100,000 on my truck by the time I got the letter.
  • troubledwaters's avatar
    troubledwaters
    Nomad
    Feb 07, 2018
    Don't know much about Chevy but it sounds like an ignition coil problem to me. Is this a Coil Over Plug (COP) design? Get a code reader and find out which cylinder has the most misfires. It probably will be like 10 times more misfires then the next closest one, this is a good indication it is the COP (or it could be the plug but less likely).
  • LIKE2BUILD's avatar
    LIKE2BUILD
    Explorer
    Feb 07, 2018
    Remove the idle air control valve and thoroughly clean it and the cavity. A sticky valve with respond to the ECM properly but not physically move. So, you can get odd idle behavior like you saw but never trip a check engine light.

    My FIL had a chevy van that was racing at idle. He could go 45MPH and never press the throttle and had no check engine lights. I replaced the AIC and all was good.

    KJ
  • Thunderbolt's avatar
    Thunderbolt
    Explorer
    Feb 07, 2018
    enblethen wrote:
    Sounds like a vacuum leak. Some vehicles have a thermal control vacuum sensor. Go over the vacuum line diagram under the hood. Look for a thermal valve.


    I am going to check it out more after work. It appears that the intake manifold gasket is a very common problem with these trucks as well. Usually the vaccum leak goes away once they are warm though unless mine is really bad ?
  • enblethen's avatar
    enblethen
    Nomad
    Feb 07, 2018
    Sounds like a vacuum leak. Some vehicles have a thermal control vacuum sensor. Go over the vacuum line diagram under the hood. Look for a thermal valve.

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