high neutral rpm

Discussion in 'Gen 1 & 2 - Engine, Exhaust, Drive Line & AC syste' started by shaldaya, Jan 18, 2021.

  1. shaldaya

    shaldaya Member

    Joined:
    Mar 2, 2020
    Messages:
    51
    Likes Received:
    9
    Location:
    Utah
    don't know if its normal, but my car idles around 2,000 while i am moving (in neutral) but drops and bounces between 1,000-1,500 when I push the clutch in, and when I come to a stop (clutch out) it settles at 1,000.
    any ideas what could cause this?
    I'm not worried about it since its been doing that for a year, but its kinda getting annoying

    I'm driving an 89 with 3.2 engine
     
  2. luigisho

    luigisho SHO Member

    Joined:
    Nov 2, 2001
    Messages:
    10,787
    Likes Received:
    3,513
    Location:
    va beach,va
    Home Page:
    Might have the idle adjustment screw off a little. Usually I'd point to Idle air sensor/valve but maybe the swap had a screw or cable movement? Could still be the IAC. Is the throttle body butterfly stuck open a little with build up?
     
  3. shaldaya

    shaldaya Member

    Joined:
    Mar 2, 2020
    Messages:
    51
    Likes Received:
    9
    Location:
    Utah
    my only question now is, where is the idle adjust screw.
    If this is the problem, it would the first time I've ever had it and the 89 sho shop book does not say anything about the adjustment screw
     
  4. luigisho

    luigisho SHO Member

    Joined:
    Nov 2, 2001
    Messages:
    10,787
    Likes Received:
    3,513
    Location:
    va beach,va
    Home Page:
    That should be the last move. Idle air control and vacuum leak should be ruled out first. I haven't looked at the TB area in a long time. I'd have to go and look under the hood. (car parked 40miles away)
    Also, was this swapped motor running and did not have this issue in this car before? ie was it running properly over time and then started acting up? If so, then the idle screws are not the issue. If it always did this, then you have to eliminate vacuum leak and faulty IAC/IAB and then look at potential throttle cable throttle body error after all normal isses are eliminated. You can swap a known working idle air control valve from any other GenI /GenII if you have some available to you.
     
    Last edited: Jan 22, 2021
  5. shaldaya

    shaldaya Member

    Joined:
    Mar 2, 2020
    Messages:
    51
    Likes Received:
    9
    Location:
    Utah
    I have a new IAC on order from rockauto, so I will try changing that, over the weekend though, I will look for a vacuum leak
    and the motor before was good (trans went out) but it was sitting for a LONG time before I installed it. but I have since done an overhaul on it, and been driving it daily for probably a year now
     
  6. luigisho

    luigisho SHO Member

    Joined:
    Nov 2, 2001
    Messages:
    10,787
    Likes Received:
    3,513
    Location:
    va beach,va
    Home Page:
    Yeah. My issue is was the idle normal for a while after the transplant, or was it always a little off? If the idle was normal, then the throttle body and cable should be ok (minus possible carbon build up. I didn't notice alot of buildup at the throttle plate on my GenI and GenII cars vs my v8 GenIII-- which got caked and sticky when pushing the go pedal a few times that required some cleaning.
     
  7. shaldaya

    shaldaya Member

    Joined:
    Mar 2, 2020
    Messages:
    51
    Likes Received:
    9
    Location:
    Utah
    to be honest, I think the was a little off before the transplant, but that was a year ago, and i've only owned this sho a year and a half, so i am unsuure
    I personally think it could be the MAF, but I have tried spraying it with brake cleaner, and have changed it once (though I might have put on another bad one), and no noticeable change
     
  8. luigisho

    luigisho SHO Member

    Joined:
    Nov 2, 2001
    Messages:
    10,787
    Likes Received:
    3,513
    Location:
    va beach,va
    Home Page:
    That's possible. I've had swapped parts and new aftermarket parts that are bad out of the box. Frustrating because you cross those off the problem list in your head. If you unplug the MAF it will run in a default mode and throw a MAF code. This will not run great, but it should stop fluxuations with bad data being used from a failing sensor to calculate air:fuel. So the thinking is, if MAF is an issue, the hunt for idle should smooth out.
     
  9. luigisho

    luigisho SHO Member

    Joined:
    Nov 2, 2001
    Messages:
    10,787
    Likes Received:
    3,513
    Location:
    va beach,va
    Home Page:
    I wonder what the vss does other than drive the speedo cable? I think I used to know but have forgotten. Does it provide input for idle or other running data? Maybe that is a 2fer for your speedo issue. Unless you can hear the internal speedometer making scraping noises in the dash.
     
  10. BaySHO Performance

    BaySHO Performance SHO Member

    Joined:
    Feb 25, 2001
    Messages:
    403
    Likes Received:
    350
    Location:
    SF South Bay
    Home Page:
    Adjusting the idle screw has been mentioned. It's on the TB, on the rear. Years ago I attempted to adjust idle via the screw but it didn't make any difference.

    Doesn't sound like a vacuum leak, but I suggest pulling the codes and checking out the IAC and TPS. Tests for those can be found here. IAC is called IAB / ISC/BPA:

    https://www.dropbox.com/sh/kxsgo4m0a51fkp5/AADEWPeuPLNRyXE8TBUK6N02a?dl=0
     
  11. shaldaya

    shaldaya Member

    Joined:
    Mar 2, 2020
    Messages:
    51
    Likes Received:
    9
    Location:
    Utah
    definitely not idle air control. I just changed it, and nothing

    also i have checked codes (for other reasons) and nothing has ever come up for air
     
  12. luigisho

    luigisho SHO Member

    Joined:
    Nov 2, 2001
    Messages:
    10,787
    Likes Received:
    3,513
    Location:
    va beach,va
    Home Page:
    You have a donor car? My next suspicion is vacuum leak. Maybe a small one. Small hose maybe?? other bad guess is computer small malfunction. Bad sensor input. This would be easier with OBDII data reading but nah.
    I guess a fuel pressure regulator malfunction could alter idle but I have never had that happen to any of my vehicles. maybe an exhaust manifold leak or O2 sensors not reading correctly? Spitballing everywhere here.
     
  13. FastCAD

    FastCAD SHO Member

    Joined:
    Feb 22, 2015
    Messages:
    132
    Likes Received:
    59
    Gender:
    Male
    Occupation:
    "cruisin'... into the sunset"
    Location:
    Miami, Florida
    Try this.
    Warm the engine up to operating temp. (2 minutes or so). Turn the hvac off. Turn off the engine. Remove the IAB connector. Start the engine (this might take a little throttle). Let the engine re-learn it's base idle "800" rpm. The (tiny idle) screw is adjacent to the spring loaded throttle body lever at the throttle stop block. Re-connect the IAB.
    If you still have a problem check your codes or clean them out to let your ECU re-learn and try this again.
    Note: the IAB will NOT throw a code.
    Best to ya.
     
    shaldaya likes this.
  14. shaldaya

    shaldaya Member

    Joined:
    Mar 2, 2020
    Messages:
    51
    Likes Received:
    9
    Location:
    Utah
    my 89 only has knobs for heat and AC. Would that make a difference?
    and the idea of warm it up first actually makes a lot of sense, but I will likely disconnect the battery also. Thanks for the suggestion
     
  15. shaldaya

    shaldaya Member

    Joined:
    Mar 2, 2020
    Messages:
    51
    Likes Received:
    9
    Location:
    Utah
    Yup
    Computer reset did he trick
    It was an ID ten T error (ID10T)
     
    Last edited: Jan 28, 2021
    luigisho likes this.

Share This Page

If you wish to help keep SHOforum running, please click the donation button below