Help, please rough idle

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

  1. kinson33

    kinson33 Member 1 Year 100 Posts

    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.
  2. TimTom64b

    TimTom64b Epic Member 5+ Years 500 Posts ROTM Winner

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

    RayVoy Epic Member 5+ Years 5000 Posts

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

    sfdefender24 Rockstar 4 Years ROTM Winner 100 Posts

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

    TimTom64b Epic Member 5+ Years 500 Posts ROTM Winner

    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.
  6. kinson33

    kinson33 Member 1 Year 100 Posts

    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...

    - - - Updated - - -

    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
  7. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    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.
  8. kinson33

    kinson33 Member 1 Year 100 Posts


    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
  9. moogvo

    moogvo Epic Member 5+ Years 1000 Posts

    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.
  10. kinson33

    kinson33 Member 1 Year 100 Posts

    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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