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Idle stuck at 3000 rpm

This is a discussion on Idle stuck at 3000 rpm within the External Engine forums, part of the LSx Technical Help Section category; Ok so cars stranded with idle at 3000 rpm. No vacuum leaks anywhere. Ive cleaned the throttle body and iac ...

  1. #1
    Mad Fabricator Z34LS1's Avatar
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    92 LS1 Lumina A4
    00 Formula WS9

    Idle stuck at 3000 rpm

    Ok so cars stranded with idle at 3000 rpm. No vacuum leaks anywhere.
    Ive cleaned the throttle body and iac this morning and inspected maf and it looks good. Can't find an iac motor anywhere locally, but have found a tps sensor gonna try that. Any other ideas? Please? $100 for the flatbed...
    Last edited by Z34LS1; 06-30-2012 at 07:44 AM.

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    Mad Fabricator Z34LS1's Avatar
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    92 LS1 Lumina A4
    00 Formula WS9

    TPS sensor not the problem either. I think it may be my spark plug wires, they are brand new 9mm wires but the ends don't fasten on as well as the factory ones. I pulled 7 of them off and every one had water in the end by the coils. The boots don't seal up like original ones. I washed my car before this happened, but don't see how water could have gotten in since I only misted the motor.

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    Moderator 98TransAmWs-6's Avatar
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    It could be you map sensor on the back of the intake. Have you taken your intake off recently? When my map sensor was busted it did something similar but it wouldn't stay started. The IAC is on the throttle body by the TPS. I would try replacing both the TPS and IAC. Since it sounds like an idle issue.
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    Mad Fabricator Z34LS1's Avatar
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    92 LS1 Lumina A4
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    I hate it when threads are Incomplete, I mean you start reading about a similar problem and the OP most often never comes back with the Fix!

    THIS THREAD IS NOT THAT WAY. I WILL POST THE FIX.

    I believe your right. I paid $135.00 for the Flat bed tow, had to push my car to a spot where the nose pointed up to get it on the bed.

    Today I replace Every Vacuum line except for the one you mentioned but I felt it and it feels good, and no I have not had the Intake off recently. The Brake Booster is also holding it's vacuum.

    I Did pull the Throttle Body and Cleaned it off the car. Pulled the IAC motor and noticed the Plunger was all the way retracted, from the mounting surface it was only extended to just under 1 Inch. I looked in the port where it goes and noticed that with the plunger retracted it will let air come into the Throttle Body via PCV lines! WALA there's my Vacuum Leak, or at least thats what I am seeing.

    Next I pulled every Plug and they looked great, then I replaced the TPS cause it was cheap and they had it...didn't need it though, it's not the problem.

    So I cleaned the IAC Motor again after paying for a new one that's not available anywhere!!!!!!!! Ridiculous! ........Anyways Cleaned it and then with it plugged into the harness but not the Throttle body I turned the key and the Plunger moved out ever so little. So I disconnected the Positive wires from the Battery, Turned the Key to on position and touched my positive lead to the fuse box Jumper terminal to the Battery and it moved a bit more, repeated this again and it extended lots more but stopped. tried a few more times and it started to move again. After it looked like it was out a ways I put the IAC into position and noticed the plunger was extended enough to seat in the pocket. Next I bolted it in and unplugged it so it would stay in position, hooked up my battery wires and started it up. It Idled rough at around 550rpm, next I plugged the IAC in while still running and the idle picked up to about 900rpm. After a few minutes the motor started warming up and the Computer took over, the idle shot up to 3000 again!

    I shut it down and pulled the iac and noticed it's fully retracted again.

    Maybe someone here can Explain what's going on with the IAC and how it gets its signals and how it works the Plunger???

    Hopefully it is the IAC motor it seems as if it only runs one way decently, thats retracting it, and I think it's broke because it retracts it so far.

  5. #5
    Mad Fabricator Z34LS1's Avatar
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    92 LS1 Lumina A4
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    An IAC (idle air control) motor is designed to adjust the engine idle RPM speed by opening and closing an air bypass passage inside thethrottle body. The cars computer or PCM (powertrain control module) receives information from various sensors and will output signals to adjust the idle air control motor in or out to adjust engine idle speed by controlling engine idle air. An idle air control motor can fail one of two ways, either the motor short circuits and stops working or the motor will develop high resistance and cause the idle air control motor to react slowly, either failure can cause the engine to stall at idle. When a trouble code scan is performed it sometimes won't always detect a failed or weak idle air control motor.



    To check the idle air control motor remove the unit, with the wires connected turn the key to the "on" position without starting theengine, the idle air control should move in or out. If the idle air control motor does nothing it has probably failed, replace it with a new unit and recheck system. Note: while the idle air control motor is removed clean (use aerosol [COLOR=green !important][COLOR=green !important]carburetor [COLOR=green !important]cleaner[/COLOR][/COLOR][/COLOR]) the passages the idle air control uses to control idle air speed, also inspect the idle air control for a build-up on the seating (pointed) end and clean as necessary.

    Idle Air Control Valve (appearance will vary)



    Common Problems
    An idle air control motor is highly susceptible to carbon and coking build up; if an idle air control goes too long without cleaning it can cause stalling and poor idle quality. Some cars are designed with a large vacuum transfer hose that connects the intake manifold to the idle air control motor. If a broken or dilapidated these vacuum lines can cause the engine to lose vacuum which will allow the engine to run rough and die. Inspect all engine and accessory vacuum lines to look for missing, torn or dilapidated lines and replace as needed. Any car that is designed with a magnetic non-motor operated idle air control like Toyota and Lexus is subject to carbon and should be cleaned about every 40,000 miles to avoid stalling.



    Basic Maintenance
    To check the idle air control motor remove the unit, with the wires connected turn the ignition key to the "on" position without starting the engine, the idle air control should move in or out. If the idle air control motor does nothing it has probably failed, replace it with a new unit and recheck system. Note: while the idle air control motor is removed clean (use aerosol [COLOR=green !important][COLOR=green !important]carburetor [COLOR=green !important]cleaner[/COLOR][/COLOR][/COLOR]) the passages the idle air control uses to control idle air speed, also inspect the idle air control for a build-up on the seating (pointed) end and clean as necessary.

  6. #6
    Spaz is My Mentor SMWS6TA's Avatar
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    Last time mine did that I had to replace the battery and alternator. Both died on me and threw the PCM into "limp" mode I thought the Alternator was good but it was fried from the power steering leaking fluid form the high pressure hose going into the reservoir. An O-ring failed.

    Check that too.

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    Mad Fabricator Z34LS1's Avatar
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    I tell you what 3000rpm is right where she starts pulling hard.
    If I had of done normal maintenance on the TB & iac I'd of saved myself se money.
    Best thing is no one got hurt. My disc brakes were Grumbling trying to hold it back.
    New chrome headers were glowing, they look old now!

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    Mad Fabricator Z34LS1's Avatar
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    92 LS1 Lumina A4
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    Quote Originally Posted by SMWS6TA View Post
    Last time mine did that I had to replace the battery and alternator. Both died on me and threw the PCM into "limp" mode I thought the Alternator was good but it was fried from the power steering leaking fluid form the high pressure hose going into the reservoir. An O-ring failed.

    Check that too.
    Good point, Mine was good and I removed it before spraying any cleaner on it. Keep in mind some rubbers don't react well to Solvents. I cleaned my o-ring off with a rag wet with wd-40.

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    Mad Fabricator Z34LS1's Avatar
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    Got my new IAC motor installed a few moments ago and now she idles like a Champ.

    My Cause of High Idle was Due to the IAC Motors Movement being "Stop & Start", The New IAC Motor Extends Smoothly.
    My Starts are Unbelievably smooth now, I had to stop and start it about five times because it fires up so quickly now and sound Very Smooth on IDLE.

    Cleaning Did not Work for me But remember my TB was Way Past being Serviced.

  10. #10
    Spaz is My Mentor SMWS6TA's Avatar
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    Glad to see you found the cause.

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