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Very rough idle

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by TwoCrowsDesign, Jul 17, 2001.

  1. TwoCrowsDesign

    TwoCrowsDesign 1/2 ton status

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    A vexing problem on my 89 350 TBI stock motor. I have had a rough idle, engine often dies in between going from reverse to drive. Its always worse when in gear with NO throttle. I have gotten code 33 and 45, replaced the o2 sensor and fixed the 45, but been unable to resolve the 33. I have replaced the MAP sensor, plugs, wires, cap & rotor. Replaced the distributor module about a year ago while having a problem very similar to this, but don't think I should be replacing that annually. Maybe I need one of them high dollar ignitions? I'm already setting my wife up for the Flowmaster exhaust next payday!

    Pretty sure this is ignition-based problem, any thoughts? Think a hotter coil would help?

    John

    <P ID="edit"><FONT class="small">Edited by TwoCrows on 07/17/01 08:59 AM.</FONT></P>
     
  2. Emmettology 101

    Emmettology 101 3/4 ton status

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    A 33 is the O2 sensor? If so and you replaced it, did you reset the computer? If y ou didn't the code will stay in memory and set off the light!

    <font color=green>MIKE</font color=green> - "Hukd on fawnics,werkd fer me!"
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  3. TwoCrowsDesign

    TwoCrowsDesign 1/2 ton status

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    Oops, I mixed up the two codes. Yeah, I cleared the 02 codes, but am now still getting the MAP code. MAP is new so problem is elswhere... What a PITA.

    JB
     
  4. Thunder

    Thunder 3/4 ton status

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    Have you checked all your vacume lines? one may be cracked or disconnected

    <font color=orange>GOT HORSEPOWER?</font color=orange>
     
  5. HarryH3

    HarryH3 1 ton status Author

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    Don't just throw parts at it. The codes just tell you what sensor is sending an incorrect value. They don't neccesarily mean that the sensor itself is bad. A bad vacuum leak will set the error code for the MAP sensor. Get a good service manual that has the troubleshooting steps for each of the codes. The savings in parts will pay for the manual. [​IMG]

    <font color=black>HarryH3 - '75 K5</font color=black>
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  6. 90K5

    90K5 1/2 ton status

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    Sounds like a vacuum problem to me.

    90K5

    See my truck at <a target="_blank" href=http://albums.photopoint.com/j/Albumindex?u=1329584&a=9886502>http://albums.photopoint.com/j/Albumindex?u=1329584&a=9886502</a>
     
  7. realsquash

    realsquash 1/2 ton status

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    OK, code 33 could mean a couple things. First of all, the MAP sensor could be bad, which it sounds kinda like to me. Second, it could be reporting the error because something else in the EFI system is making it run with abnormally low vacuum for 5 seconds.

    The error 45 means rich O2, not bad O2. The O2 could have been bad, but more than likely it was just reading rich because something else in the EFI system was making it run rich. This code has a limit of 5% TPS, so that means at idle it runs horribly rich for 60+ seconds.

    What does all this mean? To me it means that something else is wrong in the EFI system:

    A. Stuck injector(s). Hook timing light up to #1 spark plug wire and point it at the injectors' fuel spray at idle speed. If the spray patterns are not the same, or vary wildly, you have bad/stuck injectors. These things pulse normally.

    B. Super-hi fuel pressure: get it checked somewhere. could be as simple as a pinched return line.

    C. Maybe the MAP sensor is actually bad, causing it to run in limp mode, causing it to run pig rich.

    Let us know how it goes. My money is on fragged injector(s).


    Squash
    <a target="_blank" href=http://www.trailrunners4x4.org/users/realsquash>http://www.trailrunners4x4.org/users/realsquash</a>
     
  8. Motoronbrain

    Motoronbrain Registered Member

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    I'm with 90K5, check intake gaskets by spraying starter fluid down the intake manifold sides. If idle rises gaskets bad,if no change in idle gaskets good.
     
  9. TwoCrowsDesign

    TwoCrowsDesign 1/2 ton status

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    Wow, great feedback. I've checked all vacuum lines and unless I'm missing something (a distinct possiblitity), then they're ok.

    Yeah, I've got the Heim manuals and have chased through the diagnostic, still haven't narrowed it down though.

    I like the timing light to injectors suggestions and will do that tonight.
     
  10. rich'90

    rich'90 1/2 ton status

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    Could be the idle air control valve too. Try the other stuff first though before you go buy more parts. I had a rough idle and a new IAC fixed my problem, I was getting no codes though.

    Good Luck

    Rich

    Go heavy or Go home[​IMG]
     
  11. TwoCrowsDesign

    TwoCrowsDesign 1/2 ton status

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    Well, I looked at the injectors today and you were right - they are clearly not pumping at the same rate. The right one is barely spraying, while the left is going gang-busters. I think I'll yank one from my 88 and replace. Now, my dilemma, I can't find a TBI service kit in stock anywhere. I've tried everything from my "solid" local parts guy to the weinies down at AutoZone.

    I'm assuming these kits include the 4 O-rings, and 2 gaskets, but for $60 they must include other pieces as well. Do they have replacement screen filter for the injectors? Other things?

    Thanks,

    John
     

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