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Help, please rough idle

Discussion in 'GM Powertrain' started by kinson33, Dec 11, 2012.

  1. kinson33

    kinson33 New Member

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    Just put in the new spark plugs and wires as well as cold air intake. Was idling roughly before and immediately after the install all seemed well. This morning it was about 10 degrees out and I fired it up. Very rough idle, loud ping noise, I guess that's what misfiring sounds like? Revs were up and down, once I'm moving down the road it's fine. Come to a stop light and the revs dip again feeling like its going to stall. Sound like an idle air valve problem? Just bought the damn thing and the check engine light was on for the catalytic converters. So I'm not sure if the CEL is on now for something else.
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  2. TimTom64b

    TimTom64b New Member

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    My guess is that its running lean... Hence the codes on the cats. Probably the MAS.
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  3. RayVoy

    RayVoy Active Member

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    The best approach is to pull the codes and come back here with each code (if there is more than one)
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  4. sfdefender24

    sfdefender24 New Member

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    If you have the codes, check out obd-codes.com and ask here, someone will be able to help you.
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  5. TimTom64b

    TimTom64b New Member

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    Yes get the codes... This will verify. I am guessing lean as it would be rare for the two to be tripping otherwise. I have a feeling it will be lean on bank 1 and bank 2. This is what my sons truck did when is MAF failed.
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  6. kinson33

    kinson33 New Member

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    Banks 1 and 2 both running lean. Just had it read at AdvanceAutoparts.

    Just put on the new intake, could it be the computer needing to be reset? Only happens in the morning, after driving it for 10 mins and getting it up to operating temp it runs just fine...

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    Just refitted the air intake, unplugged the battery to reset the computer, and replaced the PCV. Guess we'll find out tomorrow morning if that helped anything. Keep you guys posted
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  7. RayVoy

    RayVoy Active Member

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    The PCM controls the air/gas mixture when the engine is cold, as it warms, the control is switched to the O2 sensors. The O2 sensors are changing the fuel mix so the engine will run smooth. A fuel delivery program, in the ECM, provides the injector info while the engine is cold, sounds like it is an air problem.

    Take a 2nd look at TinTom64b 's suggestion.
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  8. kinson33

    kinson33 New Member

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    Update:

    fired it up this morning after refitting the intake, replaced the PCV, and unplugged the battery. Much smoother but still not where it should be. So maybe the MAF has gone bad? Is there a way to test that before purchasing?

    to be able to get the code for the MAF not working I would have to run the scan when the engine is cold, correct?
    Last edited: Dec 12, 2012
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  9. moogvo

    moogvo Moderator

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    This just a problem at idle, or does it run like crap all the time? Pull the codes before buying anything. It sounds like an Idle Air Control valve to me.Try to clean it. You might also take a look at your throttle plates. They get really cruddy after a while and can cause bad and erratic idling too.

    Kinson, you want to scan the vehicle after it goes into closed loop mode. If it has set a code, you can read it when the engine is cold, but it is best to let it warm up so you can look at the data while it is running.
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  10. kinson33

    kinson33 New Member

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    Runs great after it warms up which leads me to believe its the MAF as suggested since it switches to the o2 sensors after getting to operating temp.
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  11. Pikey

    Pikey Moderator

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    You can buy a can a MAF sensor cleaner and try it. It is worth the $8.
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  12. kinson33

    kinson33 New Member

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    Yeah, I'll swing by the store tonight and hopefully that will clear it up and save me $$ for a new MAF
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  13. moogvo

    moogvo Moderator

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    Coolant temp sensor is a more likely candidate if you aren't getting a check engine light. There are 2 of them. One for the gauge and one for the ECM. The one for the ECM is in the intake next to the thermostat housing.
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  14. kinson33

    kinson33 New Member

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    I do have a check engine light, or did, before today for the cats being bad. On constantly, just put on the new y pipe. Light was off but the engine was warm. If the light comes back tomorrow ill know its the MAF. The codes were for both banks running lean and multiple misfires detected. Shop cleared the codes, cleaning the MAF sensor tonight and ill know tomorrow morning if I need to drop cash on a new sensor, fingers crossed.

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    Hoping you're right but that its just dirty, not needing replacement

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    No dice, after cleaning the MAF sensor lastnight fired it up this morning and the check engine light came on, heard it misfire 2 or 3 times. The light turned off after the engine warmed up.

    P0170 bank 1 lean
    p0174 bank 2 lean
    p0300 random misfire detected

    looks like ill be spending a few bucks on a MAF sensor :(
    #14
  15. Pikey

    Pikey Moderator

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    Check out some of the site sponsors like AutoAnything. There prices are usually pretty good
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  16. RayVoy

    RayVoy Active Member

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    Now we have something to work with. Codes are the first thing that should be presented when anyone has a problem.

    The random misfire maybe the first area to look at. You talked about the sound of a misfire in the original post, but I didn't think you actually had a mis-fire (no code/flashing CEL, was discussed). As you appear to be aware, the misfire will destroy the cat(s). The misfire, along with the bad cats will cause a lot of fuel ratio problems. My advise is to fix the misfire and get new cats. Forget about chasing the lean bank 1 and 2 problem until you have fixed the known problems.

    Recheck the wires, are they connected in the correct firing order, are they properly seated on the plug and the connector?

    Did you buy a wire set that was terminated at both ends, or did you cut the wires and terminate them yourself?

    What brand of plugs did you use?
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  17. kinson33

    kinson33 New Member

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    cant mess up the firing order, they're straight down... Msd wires and auto lite iridiums. Greased and all seated nicely. CEL was on the whole time but didn't get the codes until I got the new cats installed yesterday. Cel stayed off after that. Fired up again this morning, cel came back on then turned off after the engine warmed up a little (4 mins of running) which led me to believe its the MAF like someone mentioned since all symptoms go away after its warm and relying on the o2 sensors info

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    Also, if it were a plug or wire issue it would be running like crap even after it warmed up?
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  18. moogvo

    moogvo Moderator

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    You need to understand that during open loop operation (initial running before engine heats up) that the ECM completely ignores all sensors and runs directly from per programmed fuel tables. Sensors cannot set a code until the system goes into closed loop mode unless they are completely missing or disconnected.

    You seem to be sold on the idea of the maf needing repaired. I don't think that is your issue. You can clean/replace it if you want, but at this point, it is just wasted effort until you fix the misfire. Fix the known first, then worry about residual issues afterwards.
    #18
  19. kinson33

    kinson33 New Member

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    plugs went in no issues, wires clicked in place, they were already terminated, all wires correspond to correct plugs. What would cause misfire on start up but then run normal at operating temp? That's why I'm stuck on an air issue
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  20. TimTom64b

    TimTom64b New Member

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    Allot of things can cause the misfire... Assume your rotor and cap have been replaced? A beginning to fail ignition control module... Pretty much functions as a condensed in the newer ignition systems can cause a misfire too. A MAF life is rated at around 50k miles... After that they start to degrade. MAF sensor when it really fails the will run like crap no matter the temp... And RPM. With my boys truck we replace all the o2 sensors, temp sensor, cap rotor, wires and plugs... I was at wits end... And then changed the MAF sensor as a last resort before taking it to a shop... Walla... All was good.
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