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Help, please rough idle

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

  1. Pikey

    Pikey Active Member Staff Member 2 Years ROTM Winner 1000 Posts

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

    kinson33 Member 1 Year 100 Posts

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

    moogvo Epic Member 5+ Years 1000 Posts

    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.
  4. kinson33

    kinson33 Member 1 Year 100 Posts

    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.

    - - - Updated - - -

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

    - - - Updated - - -

    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 :(
  5. Pikey

    Pikey Active Member Staff Member 2 Years ROTM Winner 1000 Posts

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

    RayVoy Active Member 2 Years 1000 Posts

    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?
  7. kinson33

    kinson33 Member 1 Year 100 Posts

    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?
  8. moogvo

    moogvo Epic Member 5+ Years 1000 Posts

    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.
  9. kinson33

    kinson33 Member 1 Year 100 Posts

    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
  10. TimTom64b

    TimTom64b Member 2 Years 500 Posts ROTM Winner Gold Member

    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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