Idle issues - 1985 Stock Supra 5mge

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  1. #1

    Idle issues - 1985 Stock Supra 5mge

    Hi everyone!
    Greetings from Brazil!
    Iím having some idle issues with my stock 1985 Supra 5MGE.

    1- Under acceleration, if I step off the gas, idle hesitate and engine drops to 400 rpm for a few seconds, then stabilize to normal idle.

    2- Iím having a high idle issue if I drive for more than an hour, rpm increases about a 100 from 10 to 10 minutes.
    One day my idle was about 1500.
    My high idle problem appears to be related on hot days and using A/C.

    Any thoughts?
    Thanks!


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  3. #2
    CelicaSupra.com Member
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    On US and likely all NA 5MGE's IIRC, there's a dashpot that slows the throttle down as it approaches idle to prevent the throttle plate from slamming shut. This keeps emissions in check as well as supposedly preventing idle from dropping too low and then having to recover. It's a single vacuum line with only a vacuum restrictor and filter to prevent it from sucking crap into it. On acceleration, it takes in air slowly to position the throttle stop at a higher RPM (2000???). Then when the throttle is abruptly released, once it reaches the dashpot stop, it slowly releases the air and allows the throttle to return to a normal idle in a couple of seconds or so.
    A/C does increase idle speed, but only from the normal 650 +/-50 to maybe 900 or so. But 1500 is way more than that. About the only things that might cause that are vacuum leaks after the AFM or possibly the ECU temp sensor on the thermostat housing or the connections to it. Note that the temp sensor for the temp gauge is a separate sensor located behind and slightly above the distributor on the head.

  4. #3
    Quote Originally Posted by ray85p View Post
    On US and likely all NA 5MGE's IIRC, there's a dashpot that slows the throttle down as it approaches idle to prevent the throttle plate from slamming shut. This keeps emissions in check as well as supposedly preventing idle from dropping too low and then having to recover. It's a single vacuum line with only a vacuum restrictor and filter to prevent it from sucking crap into it. On acceleration, it takes in air slowly to position the throttle stop at a higher RPM (2000???). Then when the throttle is abruptly released, once it reaches the dashpot stop, it slowly releases the air and allows the throttle to return to a normal idle in a couple of seconds or so.
    A/C does increase idle speed, but only from the normal 650 +/-50 to maybe 900 or so. But 1500 is way more than that. About the only things that might cause that are vacuum leaks after the AFM or possibly the ECU temp sensor on the thermostat housing or the connections to it. Note that the temp sensor for the temp gauge is a separate sensor located behind and slightly above the distributor on the head.
    Thanks!
    This is the vacuum line are you referring?



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  6. #4
    CelicaSupra.com Member
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    Yes, that's the vacuum restrictor for the dashpot. But beyond the restrictor, there should only be a short length of tubing and a filter. It should not be further connected to anything on your 85. Some earlier 5MGE's did "T" this line into one of the EGR hoses or something, but no later models do. Hope this helps.

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