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TBI idle surge, winaldl data and info, need ideas/ help please

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by FWP, Mar 5, 2004.

  1. FWP

    FWP CRS

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    Out in the garage tonight trying to troubleshoot an intermittent idle surge. This can be a royal PIA when wheeling, or at a stop light for that matter /forums/images/graemlins/laugh.gif. Here's what I know so far, not sure where to go next...

    Started the truck, warmed it to operating temp by driving around, and pulled in the garage. In park, the idle started jumping all over the place. Shut it off, got my laptop hooked up, started it up, idled fine and smooth... hmmm...

    Idling smooth
    IAC- 51
    TPS- .55V, .2%
    MAP- 35-37 Kpa (I'm at 5100 ft elevation)
    RPM- 575-600
    O2- .535-.530, stable, small adjustments seen from the INT
    Temp is stable around 193 or so, and it has gone back to open loop, Idle flag is set.

    Sounds about right to me, so while still in park, I put the rpms up to 2000 for 30 seconds or so. Let back off to idle, and surging starts.

    IAC- 65-81, never does go back to 50
    TPS- .55V, .2%, stable
    MAP- 32-40,
    RPM- 400-800
    O2- .1-.9, while back in closed loop, then after idling for a time, sets the idle flag back, but the surging continues. The O2 remains fairly high~ .7

    Here's the weird part. Turn the key off, without touching anything, wait 2-5 seconds, start it back up, back to a perfect idle again. WTF /forums/images/graemlins/doah.gif I did all the above 3 times to confirm it.

    What would reset by turning the key off? It's almost like something is resetting, and saying, I'm ok now, run like this. I'm at a loss /forums/images/graemlins/1zhelp.gif
     
  2. azblazor

    azblazor 1/2 ton status Premium Member

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    I would instrument it with a vacuum gauge and a fuel pressure guage and repeat
     
  3. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    That's text book EGR sticking open at idle. IAC is trying to compinsate for the EGR trying to stall the engine. That's why your seeing it open more with a lower idle.
    Disconnect and plug vacuum to the EGR AT the TBI. If your truck has the EGR control Solonoid you need to disconnect before that.
    Drive and repeat your test. You will throw a hard code (43 I think) with the EGR disconnected but should not effect idle readings.
    This is the same symptoms my 88 Burb had. The problem turned out to be the EGR solonoid was sticking part open. Couple drops of Air tool oil into the ports did the trick. /forums/images/graemlins/grin.gif
     
  4. FWP

    FWP CRS

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    Thanks Mark, I forgot to add, I have a fuel pressure gage permanently installed, 13 psi steady, no problems there. Vacuum is steady, no leaks.
     
  5. FWP

    FWP CRS

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    Thank you sir! I will try it. I didn't even think about egr, but it was late last night /forums/images/graemlins/crazy.gif
     
  6. camok5

    camok5 1/2 ton status Premium Member

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    Mine used to do that also, Found out it was the 02 sencer.
     
  7. FWP

    FWP CRS

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    Well, it's not EGR /forums/images/graemlins/frown.gif , did as Grim suggested, no changes, same thing... O2 sensor?? It's only 6 months old, maybe I'll just replace it, they're cheap

    Any other thoughts???
     
  8. Jays Beast

    Jays Beast 1/2 ton status

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    Do you have headers on it? Is this your pick-up or your blazer? I'm having a similiar problem /forums/images/graemlins/thinking.gif about installing a heated O2 sensor /forums/images/graemlins/confused.gif
     
  9. FWP

    FWP CRS

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    Hey Jay. No headers, stock manifolds, O2 into the pipe, left bank of the K5.
     
  10. beater_k20

    beater_k20 Banned

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    my 91 does this too on occasion. last time it did it was on the 14th, when Tim and I were playing with his K30. pull it in gear, and the idle smooths out.
     
  11. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Well, wish I could help, but no idea. Did you give Doug a call/PM?
     
  12. Thunder

    Thunder 3/4 ton status

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    The last time I had a idle surge problem it was the TB gasket. Put new ones in (TB spacer) and its been rock steady.

    Just wondering. Do you have an AIR system? Sometimes when a divertor valve is bad it can cause idle problems.

    Also maby check all the wireing connections&vacume lines

    Idle surges can be a PIA
     
  13. HarryH3

    HarryH3 1 ton status Author

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    Do you have the park/neutral circuit hooked up for the ECM? I've heard of people having idle problems when they left that circuit unhooked. The ECM has different idle parameters when it thinks it's in drive than it does when it thinks it's in park.
     
  14. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    The K5 I bought had the P/N switch unhooked when I bought it (B&M never hooked up). It caused balk/stumble problems with acceleration off idle.

    And a leaky gasket enough to cause that behavior should show up on a vacume test.

    My guess is a problem with IAC or as suggested, EGR or control solenoid. Or even ECM problems (assuming all sensors check ok). But it’s just a WAG… The book I mentioned gives details on manual testing of all the bits and pieces. I've also got a GM service "driveability manual". Your welcome to borrow either if you need them Fred.
     
  15. FWP

    FWP CRS

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    Yep, thanks Russ, I hollered over to dug right last night.. Thanks for the offer on the manual, I may take you up on it...

    Is it possible to clean the IAC? I don't have a procedure on how to remove it, clean it and get it back in right. Does anyone have that info?
     
  16. FWP

    FWP CRS

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    Thanks Dale, I just replaced the gaskets about 2 months ago, and rechecked the vacuum last night... No air, no emissions other than EGR
     
  17. FWP

    FWP CRS

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    Exactly Harry! That was one of the first things I checked- to make sure the P/N flag was operating with the shifter, no problems there...
     
  18. therobzilla

    therobzilla 1/2 ton status

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    Fred,

    The IAC is very easy to clean, remove the IAC and clean it with carb cleaner be careful not to destroy the pinthle *sp*, the end of the IAC. Then restart the motor without the IAC installed and spray the carb cleaner in the manifold where the IAC normally is. The IAC is a very sensitive sensor so don't manhandle it. It will clean up real nice with carb cleaner. Make sure the end of the IAC is not worn as to how the pinthle seats against the throttle body. Make sure when you reinstall, you reset the IAC based on the procedures in the book.

    Good luck, call if I have not made any sense???

    Rob
     
  19. K5 NUTT

    K5 NUTT 1/2 ton status

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    Course i must ask did you do anything major and or minor prior to the goofy idle?

    The wifes burb would act just fine until it warmed up..then it would bounce the idle all over the place...come to find out...i made a big boo boo when i put the motor together...so the new garage rule is no children and or wifes will be present when motors are being assembled...anyways...the boo-boo caused a slight knock in the motor....very low toned...around the oil pan rail near #5 cylinder...so basically it ran fine in open loop....then when the motor warmed up and began taking inputs from the sensors thats when the idle boo-boo started reaking havoic...

    Since its not setting a code...we'll forget our conversation about the egr passages in the manifold...which cured the burbs other tit for tat.

    How wild is the swing in rpm? My conversion allways has had a minor burp in her at idle...doesn't do it all the time..and sometimes when it acts up it can be worse than other times...when i say burp..i mean less than an 50 to 75 rpm drop/ increase...that happensso quick it makes the truck shake..usually at a light...in gear. So after running my laptop on it and saving some data which i shipped over to Howell i had them burn a chip (goes back to our stock chip vs. altitude conversation)...will finish later....child is on the loose.
     
  20. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    You checked for vac leaks right? I have also have the TBI base gasket leak and caused me issues. Fire up the truck and get out the carb cleaner and spray the base of the TBI. Also check all thos freaking plastic vac lines. You look at them worng on my 88 and they are cracked.
     

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