Rough Idle in Rain

Discussion in 'Engine & Drivetrain' started by David Smith, Aug 16, 2017.

  1. David Smith

    David Smith Full Access Member

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    I was driving home a few days ago in some rain, and when I came to a stop, I noticed that my Tahoe was idling a little rough. When I let off the brake to just idle up in traffic, the truck was jumping. Like it wasn't firing right or something? Either way, it did it the entire time it was raining. Never really noticed any difference while I was actually driving, just when I was idling in traffic. Truck was moving, but no throttle. Just idling in Drive.

    Any ideas on what this could be? Bad wires? Coil?
     
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  2. shreksbrother

    shreksbrother Full Access Member

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    Personally I would be leaning toward something loose as opposed to bad. A loose electrical connector or plug wire allowing water to splash into it during wet surface driving? Have you driven it today and it was fine? No codes, I assume?
     
  3. David Smith

    David Smith Full Access Member

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    It only did it in the rain. If it is not raining, then I have no issues. No codes either. I have had a code in the past (not during the time of the issue) for a knock sensor.
     
  4. shreksbrother

    shreksbrother Full Access Member

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    Your knock sensor (and other engine-related sensors) would be excellent places to start. I would get a tube of dialectric grease to put into the connectors before snapping them back together. This should help displace any water getting into the connector in the future.
     
  5. David Smith

    David Smith Full Access Member

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    I have been trying to put off the knock sensors since I have to remove the intake. But, I guess I will have to do that sooner than later. I will probably start with dielectric grease on all spark plugs and wires. Probably go ahead and replace them with new.
     
  6. shreksbrother

    shreksbrother Full Access Member

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    It's really unfortunate that you're not tripping a code... It's a bit of a wild goose chase at this point. You could always start with the sensors that are easier to reach... Unplug them, inspect them for cracks and/or corrosion, squirt a bit of grease in them, and click them back together.

    Like I said, since it only happens when in the vicinitity of water, I would be looking more into a loose connector rather than an actual bad part (of course, it's possible the water has caused corrosion on the part's wiring or the connector's wiring).

    Good luck hunting it down! We've had plenty of rain here in the SE US this summer, so no doubt this is a frequent issue for you.
     
    Last edited: Aug 16, 2017
  7. David Smith

    David Smith Full Access Member

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    Yeah, I am here in GA and it has pretty much been rain on a daily basis. Thanks for the help!
     
  8. Maxclass

    Maxclass TYF Newbie

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    My 2004 Tahoe Z71 flex fuel has the exact same symptom: rough idle in the rain (including car wash). Although it is throwing a P0300 Code. Did you ever find a solution? I replaced my spark plugs since then, so I know it's not those. P0300 code pulls multiple causes. Hard to pinpoint.
     
  9. Maxclass

    Maxclass TYF Newbie

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  10. David Smith

    David Smith Full Access Member

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    I never actually found a solution. I actually ended up selling the Tahoe not too long ago. it happened so rarely, that it was not at the top of my list at the time. It really didn't even do it every time that it rained. Makes me think even more that it was a loose connection somewhere.

    Hope you can find the issue with yours!
     

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