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further quick question on IACs

Discussion in 'FAST Support Forum' started by crash520, Apr 21, 2019.

  1. crash520

    crash520 Member

    Joined:
    Dec 16, 2016
    Gents, I have a Sportsman XFI 2.0 TBI system on my small block mopar. The system has been running ok since I put it on. I can reach in and hit the key and it will start up from cold. The issue I have is when it does fire up it goes to idle RPM of 800, then drops back to 250 then back to 800 and its not until a min or so later it starts to run smoothly as such. It doesn't from a cold start come up to the cold start RPM and stay there then come back to running temp RPM. At cold start i can put my finger over the IAC port and feel some vacuum however the idle doesnt die off when I do, indicating to me that the IAC is not opening to its currently required 180 etc. I have set the throttle blades at running temp so as my IAC reads around 10 at idle.
    how can I test the IAC please? I've looked down the IAC port and at key on, up to temp, cold start running etc the IAC seems to sit in the same spot. I've never been able to get it to start and flare in RPM like a modern car does.
    Additionally, hot starts, I need to slightly hold the throttle blades open, I mean slightly to have the engine fire and run, if i dont, it will fire no problems, immediately go to 800 then immediately drop back to 250 and most often stumble and stop. A very small amount of throttle blade opening and it starts and run no issue once I lift off the blades.
    Ive attached a couple of files, a zoomed in log of actual cold start, plus a key on prior to start dashboard and just after start dashboard, all COLD starts
     

    Attached Files:

  2. crash520

    crash520 Member

    Joined:
    Dec 16, 2016
    I guess the question is, when Ii put my finger over the IAC port, should the RPM change?
     
  3. fabr

    fabr Member

    Joined:
    Jan 23, 2017
    Yes,it will absolutely change rpm's if you cover the hole. I would tend to say your IAC is toast.
     
  4. crash520

    crash520 Member

    Joined:
    Dec 16, 2016
    Thanks fabr whats the test procedure? pull it out and apply voltage 5 v to it? second question is how do those coves come off the TB, the four little socket head screws obviously come out, and the cover is 'O' ring sealed to the injectors, does it pull straight back or up?
     
  5. fabr

    fabr Member

    Joined:
    Jan 23, 2017
    Sorry,I don't have those answers. SFAIK it is just a GM IAC. Shouldn't be too costly to just replace to see if the issue is corrected.
     
  6. crash520

    crash520 Member

    Joined:
    Dec 16, 2016
    Anyone? Know how to test the IAC and remove it from the 2.0 style throttle body?
     
  7. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    I can't speak for testing one, but I did replace mine a year or so ago. I have never separated the end covers off the injectors. So I must of been able to do it without dismantling anything. I may have removed the rear cover screw so it was loose, but I know I never actually physically removed the cover off the throttlebody as I was afraid to damage something. I wasnt sure how it was connected to the injectors.
     
    crash520 likes this.
  8. fabr

    fabr Member

    Joined:
    Jan 23, 2017
    The covers don't need to come off to replace the IAC. I believe it is on the side of the TB ,accessible directly. Do you know what it looks like?

    To answer the question of how the covers come off though,remove the small allen screws in each and then pull up and away at approx a 45* angle.
     
  9. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    The IAC on the 2.0 throttle body (if we're thinking of the same one) is on the rear of the throttle body tucked in behind the cover.
     
  10. crash520

    crash520 Member

    Joined:
    Dec 16, 2016
    Yes JK, it is on the rear of the TB and the rear cover/fuel rail needs to come off to get the IAC out, I believe it to be a GM IAC, is that correct and does anyone have the part number please?
     
  11. crash520

    crash520 Member

    Joined:
    Dec 16, 2016
    Ok so update to my IAC QUERY.

    I pulled the IAC from my 2.0 throttle body. I’ve ohm tested it and it reads 47 ohm across the hi terminals and low terminals, I plugged back into the harness and turned the key on and it didn’t move in, with key on it should move correct ? It doesn’t wait till crank key position to move does it?

    I’d also like to check that the ECU is powering the IAC correctly, the terminal numbers on the ECU are A- 5 and 11, B- 12 and 13, which should have what power on them please?
     
  12. crash520

    crash520 Member

    Joined:
    Dec 16, 2016
    so, I checked the voltage across the A-Hi/Lo of the harness and i got approx 9V, and then B-Hi/Lo and got similar, according to the master dash the IAC should be around 90, mid point, however with the IAC plugged in it doesnt move
     
  13. Fastmanefi

    Fastmanefi Well-Known Member

    Joined:
    Jun 4, 2011
    Location:
    Sonora, CA
    Here's some EZ-2 sensor info:
    Sensors are the same as 1993-1995 GM TBI 5.7L.
    Here are the GM part numbers:

    TPS 17106681
    CTS 25036979
    ATS 25037334
    MAP 16212460
    IAC 17113598
     
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  14. crash520

    crash520 Member

    Joined:
    Dec 16, 2016
    Thanks Rich
     

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