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Thread: Cleaned throttle body, now E38 5.3 won't idle correctly

  1. #1
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    Exclamation Cleaned throttle body, now E38 5.3 won't idle correctly

    For a little background my vehicle is a 2008 5.3 and is supercharged with a tvs 1900 blower and has a higher stall converter. I fine tuned the idle using hymey's guide and had it pretty spot on since last year...this weekend I cleaned my air filter (K&N, made sure not to drench it in oil) and also the throttle body. The truck has 125,000 miles on it and the TB was pretty gunked up with carbon and oil deposits on the back side, so I cleaned it really well, using CARB cleaner which I have since read is a big no-no on these GM throttle bodies due to a coating.

    I put the intake back together, started the truck, and noticed the throttle was extremely sensitive, as in a slight blip of the throttle gave a larger rise in rpm than I'm used to seeing and it took longer to settle back down to idle. As I drove the truck around, I noticed the idle speed in parking lots was about 1100 where before it was under 800 rpm.

    I disconnected the MAF, TB, reconnected everything, no change. I sprayed carb cleaner around the intake piping and throttle body and didn't notice any change in idle speed, so I don't think it is a vacuum leak.

    When above 2mph and 0% APP, the truck idles quite high and doesn't settle down as before. I got to thinking, since I cleaned the carbon deposits from the throat of the TB, more air is probably entering the engine than before, so I tried to tweak the tune again using my idle tweaking tune from before but I could not get the TP% to drop below 23.9% (no air or spark corrections enabled). I'm really scratching my head here, did I mess up the TB using carb cleaner?

    Attached are the tune I have been running with no changes, idle tuning tune, and some logs showing how the idle is really slow to return to 650 rpm. Timing is doing it's job as it is pulling -17 degrees to get the engine idle in check, and the TP PI controller eventually trims the TP% down to where it needs to be, I just can't get the TP% to fall below 23.9% with no corrections via tweaking B1650, B1651, B1652.

    I basically need to get the max idle area (B1651 & B1652) low enough so that the engine rpm falls just above idle speed and allows the ECM to correct small idle errors, but I can't get it to respond as expected. Please help!!

    Idle after cleaning TB, no tune change 1.efi
    Idle troubleshooting - driving and stopping, no tune change, idle reset performed.efi
    Idle tune 1 ETC area unchanged 4552.3 b1651 changed to 0.85 b1651 changed to 1.2 .efi
    Idle tune 2 ETC area changed to 4900 b1651 0.65 b1652 1.2 .efi
    Idle tune 3 ETC area changed to 6000 b1651 0.65 b1652 1.2 .efi

    MAF TUNE V1.2.ctz
    TUNING_IDLE V1.1.ctz

    -Keith
    Last edited by Stroked250r; May 5th, 2015 at 04:45 PM.

  2. #2
    Joe (Moderator) joecar's Avatar
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    Several comments:

    - sounds like PCV is letting oil get sucked into intake manifold... revise PCV system to eliminate this.

    - avoid oiled filter media, these will cause MAF sensor to get oiled (and then dust sticks to the oil)... did you clean the MAF at all (use CRC MAF Cleaner)...?

    - sounds like there is an airleak, or an airleak immediately off-idle... did you install the air hoses to the throttle body and intake manifold in their correct locations...?

    What PCV plumbing do you have...? Is it leaking...? Are valve covers leaking (air)...?

  3. #3
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    Yes I need to add a catch can system, just haven't done it yet.

    No I did not clean the maf, the top side of the airbox and inside of the maf were clean as a whistle so I didn't touch them. The only parts that were dirty were the underside of the filter and behind the throttle body.

    I did replumb the vacuum hose into the intake tube. I'll check the routing of the hose and make sure nothing loosened up on the valve cover side. I sprayed carb cleaner all around the intake and intake hose assembly and didn't notice a change in idle speed BUT maybe I didn't spray the right area.

    PCV plumbing is stock, never had an issue before this.


    Can someone look at the tune TUNING_IDLE v1.1 and let me know if I missed something in the tune? I've used a tune similar to this before (following hymey's e38 tuning guide) and I can't get the throttle to drop below 23.9% via the ETC throttle area and max idle area settings. I've maxed out minimum idle air and zeroed out any correcting tables. The throttle hangs as expected, just not as low TP% as I expected. Maybe I'm missing something.

    Thanks again!

  4. #4
    Joe (Moderator) joecar's Avatar
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    You have to log GM.ETCTP or GM.ETCTP1 or GM.ETCTP2 instead of GM.TP or SAE.TP.

  5. #5
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    Well it looks like the issue cleared itself up, not sure what changed between last night and today, maybe flashing the ECM has triggered it to recalibrate the TPS and ETC.

    With that said, I still want to figure out what's up with my idle tune and see if I can tweak it some more.

  6. #6
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    FTIW both of my LS2's did the same thing completely stock after cleaning the throttle bodies. (stock tunes as well) I had the intake off the C6 to replace the oil pressure unit and figured Ill clean it while im in there, same thing on my old CTS-V.
    About a day later it settled out. Made me wonder if there was some type of throttle body positioning reset procedure I missed or it just takes it a bit to relearn idle airflow vs spark so the dashpot isnt whacky.

  7. #7
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    The GM scan tools have a button to reset learned throttle "coking" so they'll learn faster after cleaning the TB...without it, it takes longer for it to learn to idle again.

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