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Thread: 4AGE 16V - Idle Hunting

  1. #1
    Forum Member 1st year Apprentice
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    Default 4AGE 16V - Idle Hunting

    I have a 4AGE 16V engine in my Austin Healey Sprite. At idle it constantly revs up and down (ie 800 to 1500ish to 800 etc). When I add a bit of throttle it goes away. When it is cold it is slightly worst then when warm. The standard ECU is used. I have checked the Water Temp Sensor and it is giving the correct signal to the ECU from cold to hot. I have checked the ECU for fault codes and this is OK. I have checked the T-VIS VSV and it looks like it is working OK (opens at high revs and closed at low revs). I have checked the water lines to the Throttle Body and these are all clear. The cylinder compression is OK (1100, 1100, 1100, 1050). If the vacuum line is removed from the Vacuum Sensor the idle stops going up and down. I changed the Vacuum Sensor and got no improvement. I ran a vacuum hose from another car to the vacuum sensor and got no improvement. ANY IDEAS

  2. #2
    JZ Powered Too Much Toyota EldarO's Avatar
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    Default Re: 4AGE 16V - Idle Hunting

    its your TPS, set it correctly.

    unscrew the two phillips head screws on the TPS (black plastic thing opposite the throttle on the throttle body) and swing it from side to side (the screw holes are slotted for this reason)

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    is the bestest Conversion King LeeRoy's Avatar
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    Default Re: 4AGE 16V - Idle Hunting

    Quote Originally Posted by EldarO
    its your TPS, set it correctly.

    unscrew the two phillips head screws on the TPS (black plastic thing opposite the throttle on the throttle body) and swing it from side to side (the screw holes are slotted for this reason)
    I disagree,

    Your water level is low/you have air in your system. What happens is your coolant temp sensor cant read air so tells the ecu the engine is cold and the ecu kicks in your cold start injector and makes it idle high. Once it gets wet again it turns the cold start/idle off/back down. This will happen in the space of 1-2 seconds and the idle will constantly fluctuate. Will be ok while driving though.

    Bleed your cooling system and fill it up with water and it will go away.
    Daily Driver: Red Ae93 Project: My TA22 - now with 3s-gte
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    tilting at windmills Carport Converter Ben Wilson's Avatar
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    Default Re: 4AGE 16V - Idle Hunting

    Quote Originally Posted by LeeRoy
    Bleed your cooling system and fill it up with water and it will go away.
    Definately worth a try, bouncing idle is a well known problem in AW11s, as is air pockets in the coolant...
    Strange things are afoot at the circle K

  5. #5
    i wrote the Automotive Encyclopaedia roadsailing's Avatar
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    Default Re: 4AGE 16V - Idle Hunting

    i had this exact problem, was caused by the idle up valve (controlled by coolant temp running through the TB)

    my engine didnt have any coolant running through the throttlebody, so i just plated over the bypass valve. result: 500rpm idle when cold, 1000 RPM idle when warm, fixedt he problem completely
    like to drift? live in victoria?
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    At Work I'm A Grease Monkey Hibba's Avatar
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    Default Re: 4AGE 16V - Idle Hunting

    I had the same problem with my AE86 when i had it,

    It was the intake manifold gaskets, or lack of that were causing it.

    MX83 Grande
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    Junior Member Grease Monkey cartledge_uk's Avatar
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    Default Re: 4AGE 16V - Idle Hunting

    It could be a number of things

    1. First bleed the coolant properly as mentioned above (most likely cause)

    2. If its not the coolant then check for air leaks.

    3. If there are no air leaks then it could be the waxstat (they fail all the time in the uk). take off all the intake hosing and start the car, inside the throttle body at the 5 o'clock possition is a small hole (about 2 cm into the throttle body) stick your finger over it. The the engine dies, its the waxstat. You can either replace the throttle body, or block off the aforementioned hole and install a manual choke, using any old solinoid.

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    Junior Member Backyard Mechanic
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    Default Re: 4AGE 16V - Idle Hunting

    my 1jz did the same thing it was the tps set incorrectly, when it goes back to idle it has a switch to tell the ecu its meant to be idling. If it set incorrect the switching doesn take place and give you the hunt.

    I find it hard to believe the an air bubble would constantly be causing the same issue

  9. #9
    is the bestest Conversion King LeeRoy's Avatar
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    Default Re: 4AGE 16V - Idle Hunting

    Quote Originally Posted by naten
    my 1jz did the same thing it was the tps set incorrectly, when it goes back to idle it has a switch to tell the ecu its meant to be idling. If it set incorrect the switching doesn take place and give you the hunt.

    I find it hard to believe the an air bubble would constantly be causing the same issue
    As i said before
    Quote Originally Posted by LeeRoy
    What happens is your coolant temp sensor cant read air so tells the ecu the engine is cold and the ecu kicks in your cold start injector and makes it idle high. Once it gets wet again it turns the cold start/idle off/back down. This will happen in the space of 1-2 seconds and the idle will constantly fluctuate. Will be ok while driving though.
    Sure a tps could cause similar things as this guy is describing but this is a 4age and not a 1jz. I've had the exact same thing happen on my 4age and it did exactly what this guy is describing. It turned out to be a low water level and hence air in the cooling system.
    Daily Driver: Red Ae93 Project: My TA22 - now with 3s-gte
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    JZ Powered Too Much Toyota EldarO's Avatar
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    Default Re: 4AGE 16V - Idle Hunting

    my mate had this exact thing happen on his 4A and it was TPS.

    dont be so quick to discount an idea.

    especially with no in depth knowledge of this particular situation.

    the problem with diagnosing problems is that a variety of issues can cause the same symptoms.

    guys, keep it at listing your experiences, not ideas or opinions.

    it gets to that stage if the listed options run out, then we can start guessing.

  11. #11
    Backyard Fabricator Automotive Encyclopaedia
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    Default Re: 4AGE 16V - Idle Hunting

    I've had the idle hunt problem on a few 4age's, it was caused by an incorrectly set TPS on all of them.

    When the TPS is out of adjustment it hits the "fuel cut RPM" as listed in the service manual. A quick test you can do to check if it is caused by the TPS is to unplug it while the engine is running, if the hunting stops then you need to adjust the TPS to spec, if it doesn't stop then start looking into the cooling system/Wax pellet valve etc.

  12. #12
    Junior Member 1st year Apprentice
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    Default Re: 4AGE 16V - Idle Hunting

    had this on my 4age.
    the manifold gasket was split and the manifold was cracked in 4 places.
    also check all vaccum and the map line for spilts.

  13. #13
    Mad****** Grease Monkey FASTFOO's Avatar
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    Default Re: 4AGE 16V - Idle Hunting

    It "hunts" because the tps is set right and working!!

    If it is set right and working the tps sends a signal to the computer down the "idl" pin to let it know that throttel is closed and you want it to idle and sets a rev limit of about 1800 rpm. When the revs go over that the cumputer turns off the injectors untill the revs drop to about 1000 rpm and turn back on sending the revs back up again.

    The tps has no direct control over idle speed. Infact the computer on a 16 valve 4AG has no idle controll at all or even cold start for that matter.

    So why does it idle so high? Being map sensed it will mix fuel to any air getting in the manifold from anywhere and revs will go up.

    This could be a poorly set throtle stop (although if this was the case it should drop "IDL" from the tps and just rev high)

    It could be geting air through the idle speed control valve (may be faulty or not getting water flow) Check as said before by blocking the hole in throtle body.

    Or it could be a vac leak.(would my guess)

    Regards
    MATT.

    P.S. If the manifold has had the old chop and swap for RWD it could leak internaly from the old crank breather system (usaly wistles too)

  14. #14
    Olde mechanic Carport Converter oldeskewltoy's Avatar
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    Default Re: 4AGE 16V - Idle Hunting

    Hmmmmmm, MAP sensor or AFM?


    Idle hunting diagnosis is a bit different between them.
    Information is POWER... learn the facts!!

  15. #15
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    Default Re: 4AGE 16V - Idle Hunting

    Quote Originally Posted by shinybluesteel
    i had this exact problem, was caused by the idle up valve (controlled by coolant temp running through the TB)

    my engine didnt have any coolant running through the throttlebody, so i just plated over the bypass valve. result: 500rpm idle when cold, 1000 RPM idle when warm, fixedt he problem completely
    This worked for me when i had the idle hunting problem.

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