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Thread: Idle Valve (ISCV) Cleaning, can help solve poor/erratic idle

  1. #1
    Toymods Club Member #194 Conversion King Lambolica's Avatar
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    Default Idle Valve (ISCV) Cleaning, can help solve poor/erratic idle

    The ISCV (or Idle speed control Valve) on Toyota engines is an ECU controlled valve for letting a controlled amount of air past the TB if the ECU deams it required (ie when a/c is on or Alt is loading due to heavy current draw)

    The ISCV draws air from before the TB and a solinoid type valve opens and closes as the computer needs more or less air at idle. This solonoid often becomes clogged with crappy thick oil deposits over time and eventually allows more air to pass than the ECU wants due to the inability of the valve to seal correctly.

    The followings is a pull down of an ISCV off a 1G-GTE, however 7M's and others are similar.

    This 1G had an erratic idle. It would idle find for a while, then drop down to 4-500 and sit there for a while before going back to normal. The 7M-GE had a constant low idle down around the 300 mark. I found that if i drove with the head lights on or the A/C pump on that the revs lifted slightly, I worked this out after realising the 1G only ever had the problem during the day (when I didn't have lights on)



    Here you can see the valve bolted to the side of the plenum (it is the black thing with the plug missing). This is removed from the plenum by unbolting the 2 12mm bolts and removing the air pipe and 2 waterlines.



    Here is the unit removed from the engine. the 3 screws holding the black plastic solinoid part to the cast base need to be removed.



    Once appart you can see the knob on the solinoid is quite black and to touch ( in this case) it felt very gooey and sticky and the oil layer was quite thick. you can see also the bese section has a black ring around the hole.

    These can be cleaned using a carby cleaner, WD-40, INOX, Prepsol etc. The base section is wiped clean with a cloth soaked in cleaning solution as is the knob section. the knob section is in fact made of metal even though at first glance it appears to be plastic.



    After cleaning this is what they should look like... the knob is clearly cleaner and now creates a good seal in the base. assembly is the reverse of removal, however note that the gasket to the plenum may need to be replaced so having some gasket Goo on hand might be a good idea in case.

    The results... The 1G now idles level and smooth, and the 7M is sooooo much better than it was it is hard to believe somthing so minor can cause such an annoyance.

    Please feel free to add or contradict any info here for peoples future searches
    Beige.... The new Black!!!

  2. #2
    Gary Motorsport Inc. Too Much Toyota takai's Avatar
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    Default Re: ISCV Cleaning (*May* solve poor/erratic idle)

    For those with 4AGZEs it is a big change to have a clean ISCV, and especially with long post charger intake tracts, while it doenst 100% resolve the dirty idle, it goes a long way.
    -Chris | Garage takai - Breaking cars since 1998
    Sparky - AE86 IPRA Racer | RZN149 Hilux - Parts and Car Hauler
    I never saw a wild thing sorry for itself. A small bird will drop frozen dead from a bough without ever having felt sorry for itself. - D.H.Lawrence

  3. #3
    Junior Member Backyard Mechanic ndgcpr's Avatar
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    Default Re: ISCV Cleaning (*May* solve poor/erratic idle)

    does removing the water lines require a coolant refil? Just so i know when i try and attempt it.

    good work
    Noisy Diff and Gearbox Club of Pine Rivers
    and you thought your car was loud
    The Soarer brought to you by the letter TT

  4. #4
    Current UZA80 owner Chief Engine Builder JustCallMeOrlando's Avatar
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    Default Re: ISCV Cleaning (*May* solve poor/erratic idle)

    Not a coolant refill persay, but definetly a top up, you'll lose a little bit.
    Teh UZA80 - Project Century - Remotely p00'd by association

  5. #5
    Junior Member Backyard Mechanic 82MKII's Avatar
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    Default Re: ISCV Cleaning (*May* solve poor/erratic idle)

    It might be worth actually blocking off the coolant path through the ISCV. I know on my 1J there is a coolant path that flows past the throttle body & then through the ISCV - so they can't freeze up in winter. We don't really have that problem here - so all the coolant does is heat up the manifold & hence your intake air = bad.
    If you block the hose coming out of the block & the one back into the return line, you may have a cooler inlet manifold = slightly more power, plus you don't have to hassle about losing coolant when you play with the ISCV.

    Regards

    Peter

  6. #6
    Junior Member Backyard Mechanic 3sgte's Avatar
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    Default Re: ISCV Cleaning (*May* solve poor/erratic idle)

    Quote Originally Posted by 82MKII
    We don't really have that problem here - so all the coolant does is heat up the manifold & hence your intake air = bad.
    Due to the pressure drop that occurs across the valve, a freezing problem is actually more likely than many might think.

    Of course, humidity is a needed ingredient, so point taken...

    Some later model Toyota/Lexus used an inline thermostat at the coolant hose going to the throttle body to limit the temp of the coolant.

  7. #7
    Altia ER34 GTT Domestic Engineer JetspeedCamry's Avatar
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    Default Re: ISCV Cleaning (*May* solve poor/erratic idle)

    I removed/cleaned mine last year. A word of caution is NOT to take apart the stepper motor and CLEAN the bearings inside it. There nylon packed units and don't respond well to and harsh chemicals! I learnt this when my engine kept stalling everytime i clutched in. Wouldnt idle at all. Took the ISCV apart again and the bearings where STIFF...the chemical i used to clean it all inside seized them. I WD40'd them back up and they've been ok..but never the same. But overall, cleaning it solved a low and erratic idle problem i had.
    Kind Regards,
    Kurt.

    1998 ER34 ニッサン スカイラインGT- T
    RB25DET 5 Speed Manual | Blitz SE Return Flow FMIC | Greddy Profec II Spec B BC | Apexi N1 Turbo Back Exhaust

  8. #8
    ST185 GrpA #135 Automotive Encyclopaedia Toobs's Avatar
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    Default Re: ISCV Cleaning (*May* solve poor/erratic idle)

    Note: Don't let carby cleaner or prepsol get anywhere near the rubber parts (e.g. the O-ring between the cast piece and the solenoid) as those chemicals can perish the rubber.

  9. #9
    Junior Member Grease Monkey
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    Cool Re: ISCV Cleaning (*May* solve poor/erratic idle)

    Yes, cleaning the IAC/ISC on most engines is routine maintenance.
    On Toyota's, if they just would have located every damned EGR port farther away form the IAC/ISC & throttlebody's, they would have never had a problem with them. Unfortunately... Half the manifolds have the EGR valve shooting exhaust straight at the IAC/ISC valves. Causing problems.

    To add:
    2vz-fe 3vz-fe


    1mz-fe 2mz-fe

  10. #10
    MR 18RG Chief Engine Builder The Witzl's Avatar
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    Default Re: Idle Valve (ISCV) Cleaning, can help solve poor/erratic idle

    Here's the ISCV location on a 4A-GE silvertop 20V:

    ...... butt scratcher?!


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