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do I need a new ECM?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by mrkay, Aug 22, 2000.

  1. mrkay

    mrkay Registered Member

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    My 88 Blazer (fuel injection) has been idling high since I bought it 5 months ago. I can kick it down only slightly. But it is very high even then. I checked the seal around the Throttlebody carb and replaced the Idle air control motor. No change.
    The manual says that the idle is controlled by the ECM if you have fuel injection. Is there a way to test this? This is the box that contains the computer chip and sends out the diagnostic signals. Can I get one at a junk yard?

    Any one had experience with this?

    I'd appreciate any help. My drive train is taking a beating.

    <font color=blue>Rock climbing on Plymouth Rock</font color=blue>[​IMG]
    with my 88 Blazer 350/Auto/TBI[​IMG]
     
  2. sosamantx

    sosamantx 1/2 ton status

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  3. realsquash

    realsquash 1/2 ton status

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  4. mrkay

    mrkay Registered Member

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    I just put in a new IAC - Idle Air control motor - It has a little spring tip on it. This did'nt change anything. The one I took out was gummed up with black goop.

    <font color=blue>Rock climbing on Plymouth Rock</font color=blue>[​IMG]
    with my 88 Blazer 350/Auto/TBI[​IMG]
     
  5. mrkay

    mrkay Registered Member

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    With a new IAC in I thought it would slow the idle properly. But nothing changed at all.


    <font color=blue>Rock climbing on Plymouth Rock</font color=blue>[​IMG]
    with my 88 Blazer 350/Auto/TBI[​IMG]
     
  6. realsquash

    realsquash 1/2 ton status

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    You've gotta find the IAC passage on the throttle body (the other end of the hole where the IAC mounts). The IAC does the same thing as moving the throttle plates, but only at idle. It is a "controlled" vacuum leak. Find the IAC passage and put your finger over it. If the idle speed slows down, you know you have a wiring/ECM problem (since you replaced the IAC already it prolly isn't that). The other thing is to make sure that your throttle plates are closing properly. They aren't supposed to be completely closed, but not very open. You should have an adjusting screw on the linkage on the side of the TB to adjust, but if you didn't move it, don't timker with it.

    Does the Service Engine Soon light come on at all?

    Squash
    http://www.trailrunners4x4.org/users/realsquash
     
  7. mrkay

    mrkay Registered Member

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    OK, I understand the reason for the IAC now. Since I put in a new one, the assumption is that the idle should have slowed down correctly. Since it has'nt, I'll pull it and block the hole and see if the idle slows. If it slows, do I assume that there is a mechanical problem or an ECM issue?


    <font color=blue>Rock climbing on Plymouth Rock</font color=blue>[​IMG]
    with my 88 Blazer 350/Auto/TBI[​IMG]
     
  8. realsquash

    realsquash 1/2 ton status

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    No, don't remove the IAC. There is a hole, separate from the throttle bores (but inside the air cleaner's base gasket), where you will detect vacuum if you stick a finger in it. If you find the hole and there isn't any vacuum, you have either a bad IAC, bad IAC wiring, a bad ECM, or throttle blades that aren't closing for some reason, such as drebris on the linkage, mis-adjusted set screw on the throttle lever, etc.

    I would bet on the throttle sticking open a little bit.

    Squash
    http://www.trailrunners4x4.org/users/realsquash
     
  9. River

    River 1/2 ton status

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    Is it possible that you your car has a airco that is not function good. When you turn your airco on the ECM will increase the idle speed.
    An other possibility is that the axle off your TBI is leaking vacuum.

    Goodluck.

    Greetings from River,


    River `90 K5, 350, TH700R4, NP241, "33, 3.08, 10 bolt F, 10 Bolt R
     

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