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Thread: TBI with High Idle in PARK

  1. #46
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    So today I installed a new IAC pigtail from the engine to the computer... Went through the TBI setup and with the IAC forced close and then unplugged the truck idles at 525. Plug it back in and after a few minutes back to 1000 it goes, with counts in the 50's. is there a sensor you think could be causing this? I data logged today but I'm not sure how to post it on this thread. Thanks for everyone's help, Jason

  2. #47
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    High Idle in PARK

    Not sure if I did this correctly..... but I tried!
    Attached Files Attached Files

  3. #48
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    I'm seeing 2 engine codes 15 Coolant Sensor Low and 34 MAP Low. Don't just change parts. Double check the cleanliness of the grounds to those sensors. You can use a volt meter to verify key on engine off and running volts.
    Last edited by stew86MCSS396; 08-09-2020 at 03:34 AM.

  4. #49
    Super Moderator dave w's Avatar
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    Couple Screen Shots from the New Iac Wire.xdl

    I agree Codes 15 & 34 are in the log.

    The MAP and CTS look normal on the Dash Screen.

    dave w
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  5. #50
    Super Moderator dave w's Avatar
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    I wonder what removing the Park input from the ECM connector would do to the idle. The screen shot in the previous post shows "Park" with the high idle.

    Manual Transmission 1227747 TBI systems have VSS input without the "Park" switch wiring.

    dave w

  6. #51
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    I'm going to look into the two codes and I will try removing the Park input from the ecm. The codes seem odd because no CEL ever came on... Thank again everyone and keep the thoughts coming! Keep thinking about the possibility that something was done wrong when the engine and wiring was transplanted from the donor vehicle. Jason

  7. #52
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    Well removing the park input from the ECM did not change anything with regards to the HIGH idle in park. Check that off the list!!! any other thoughts on this? is it ok to install back into the loom? thanks, Jason

  8. #53
    Super Moderator dave w's Avatar
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    Before installing the Park wire back into the ECM connector, try the following:
    Reset the codes by disconnecting the battery for 1 minute.
    With the Park wire unplugged from the ECM, codes cleared (verified in TunerPro) ... try the short cut IAC adjustment by adjusting the IAC screw so that TunerPro RT shows less than 30 steps (ideally 10 steps) with the engine fully warmed up. Verify the TPS voltage is 0.55 VDC after adjusting the IAC Screw.

    I've done the short cut IAC adjustment several times with good results. Keeping the TPS volts @ 0.55 VDC is a HUGE challenge when using the short cut IAC adjustment. The TPS voltage can fluctuate when tightening the TPS mounting screws. Adjusting the IAC screw will change the TPS voltage

    dave w

  9. #54
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    High Idle in park

    Dave,
    I followed your suggestion and got the IAC counts down around 6-9 and the TPS set very close to .55 but now the idle is 1100. I attached the log.
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  10. #55
    Super Moderator dave w's Avatar
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    I am currently out of any new ideas.

    dave w

  11. #56
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    At 6-9 counts the IAC will be nearly closed. Can you confirm that by looking at the idle air passage?

    What happens if you put you thumb over the IAC passage?
    89 K1500 Scottsdale 5.7L 5spd 3:42 RamJet cam Dart iron TBI heads 427 PCM swap
    95 C2500 Cheyenne 6.5L turbo diesel 4L80e 4:10 DB2-4911 Manual pump conversion 0411 PCM trans control 2Bar COS
    05 Outback XT 2.5L turbo gas auto

  12. #57
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    Yes, its nearly closed. but the throttle blades are waaaaaay open. If I jumper the ALDL and turn the key on, I can pull the IAC plug when the plunger is at about 20 counts, then leave it unplugged and it idles nice. I'm lean toward a new wiring harness! I don't know what else to try.

  13. #58
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    As a ballpark adjustment for the throttle blade opening, try adjusting the throttle blade opening by pulling a strip of paper about 1/2" wide x 4" long through the throttle blade opening. The paper strip should have a slight drag when pulled through the throttle blade opening.

    Note, paper thicknesses will vary depending on the paper. I use a common 20 lb paper, not 16 lb (to thin) or 24 lb (to thick).

    dave w

  14. #59
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    Quote Originally Posted by JJK10 View Post
    Yes, its nearly closed. but the throttle blades are waaaaaay open. If I jumper the ALDL and turn the key on, I can pull the IAC plug when the plunger is at about 20 counts, then leave it unplugged and it idles nice. I'm lean toward a new wiring harness! I don't know what else to try.
    If your throttle blades are "waaaaay open" and your TPS voltage is .55 you have a strange problem. What is the TPS voltage when the throttle blades are closed? Or just a turn open from closed?
    89 K1500 Scottsdale 5.7L 5spd 3:42 RamJet cam Dart iron TBI heads 427 PCM swap
    95 C2500 Cheyenne 6.5L turbo diesel 4L80e 4:10 DB2-4911 Manual pump conversion 0411 PCM trans control 2Bar COS
    05 Outback XT 2.5L turbo gas auto

  15. #60
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    I would open the butterflies, cycle the key and then reset the TPS. I continued that until the counts were near 10, at that point the idle was worse.... ]If your throttle blades are "waaaaay open" and your TPS voltage is .55 you have a strange problem. What is the TPS voltage when the throttle blades are closed? Or just a turn open from closed?[/QUOTE]

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