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  1. #1
    Sr. Apprentice Sir Koscoe's Avatar
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    Default Rough idle when cold

    Now that I have the break issues fixed it's on to my next project. In the mornings when it is cold out the truck idles rough. Roughly like I am pressing the gas and letting off until it gets warm then it runs fine. Could this be a dirty MAF and/or TB? My brother said his 99 did this same thing and cleaning the TB helped. I know it will be a good idea to clean them anyway since the truck has 184k on it. Just wanted your thoughts. Thanks.
    If you think you can do a thing or think you can't do a thing, you're right.--Henry Ford

  2. #2
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    using throttle body cleaner and removing the IAC and then clean the parts will help idle issues.I use a tooth brush and a cloth to clean and wipe out the carbon deposits as much as possible.
    the PCV and the crankcase hoses need to be checked/replaced. the ECT could be defective @180,ooomi I would replace it.

    pcm uses MAP/MAF/ECT to adjust cold start idle,,, a leak/bad PCV in the crankcase venting or other vacuum leak throws off these programed PCM idle control. also leaks in the air intake after the MAF.

    I would get crc MAF cleaner and clean the small maf sensing wires. just a small amount of spray on the wires is all that is needed. do not touch the wires.

    hold the throttle body open to dry out the throttlebody cleaner before starting. If its cold out use a hair dryer to evap the solvent before starting.

  3. #3
    Sr. Apprentice Sir Koscoe's Avatar
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    Quote Originally Posted by j cat View Post
    using throttle body cleaner and removing the IAC and then clean the parts will help idle issues.I use a tooth brush and a cloth to clean and wipe out the carbon deposits as much as possible.
    the PCV and the crankcase hoses need to be checked/replaced. the ECT could be defective @180,ooomi I would replace it.

    pcm uses MAP/MAF/ECT to adjust cold start idle,,, a leak/bad PCV in the crankcase venting or other vacuum leak throws off these programed PCM idle control. also leaks in the air intake after the MAF.

    I would get crc MAF cleaner and clean the small maf sensing wires. just a small amount of spray on the wires is all that is needed. do not touch the wires.

    hold the throttle body open to dry out the throttlebody cleaner before starting. If its cold out use a hair dryer to evap the solvent before starting.

    Thanks Cat. The truck runs good after it warms up, so i will clean everything when it gets a bit warmer out unless the issue becomes worse.

    Dumb question, but will this affect my MPG's?

  4. #4
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    lets say you have a failure with the crankcase vent system which causes a loss of the calibrated measured Vacuum of an amount GM used to program the PCM. then the PCM will see that the engine is with a lean condition now it opens the injectors for a longer time to correct to get the 14.7 to 1 air to fuel ratio.

    this causes lower MPG.

    after the cleaning and checking for any vac failures the engine should idle smooth and with the maf cleaned faster throttle response

  5. #5
    Sr. Apprentice Sir Koscoe's Avatar
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    Quote Originally Posted by j cat View Post
    lets say you have a failure with the crankcase vent system which causes a loss of the calibrated measured Vacuum of an amount GM used to program the PCM. then the PCM will see that the engine is with a lean condition now it opens the injectors for a longer time to correct to get the 14.7 to 1 air to fuel ratio.

    this causes lower MPG.

    after the cleaning and checking for any vac failures the engine should idle smooth and with the maf cleaned faster throttle response

    Awesome. I can't tell if the truck has a vac leak of a small miss. You can hear it while I am on the throttle. I need to give the engine bat a really good check once it warms up outside. I don't want to freeze my boys off since I have no garage of my own to work in.

  6. #6
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    looks like the nasty cold is not coming back too soon 40's up here. the 3 ft of snow we got last week is down to about a foot. nice weather now.

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