Question about 1990 Isuzu Trooper

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Idle speed too high

Isuzu trooper LS 1990, V6 2.8L TBI GAS

The idle speed is too high, even though the IAC valve is new. I must be 800 rpm and it is as high as 1300rpm.

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  • harpsterearl Dec 14, 2008

    1992 isuzu wont start

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  • 93 Answers

Look under the plastic intake tube for a hole

Posted on Nov 19, 2008

  • jessaboo Nov 13, 2010

    For the non-car savvy, could you please clarify? Intake tube: Fuel or air?
    Under the air filter in throttle body assembly? or on its way to TB from either fuel line or air intake, respectively?
    This seems a common problem with these otherwise fun trucks and would be great to have this be available to owners with this problem. My truck will some days idle perfectly. -which sometimes coincides with a very low tank of gas - which leads me to believe it could be a fuel delivery issue.. (Pump/regulator, etc..) but other times it will idle close to 1800 rpm's!! -Wtf??
    Maybe their just moody. -My truck's a girl for sure, but I love her! ;)

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The normal idle speed is below 1,000 rpm...between 800 to 900 rpm. I suspect that the idle-air control motor has seized and can no longer automatically adjust the engine's idle speed. This part is also responsible for slightly increasing idle speed when the airconditioning is switched on to compensate for the added engine load. Some cars even have a "step-up" solenoid to increase idle.

When replacing the idle-air control motor, remember to clean the port that IAC motor goes into; there will be some carbon build-up that may prevent the part's cone-shaped valve from seating properly. A can of intake valve spray helped along with some Q-tips works well.



Hope this helped.

Have a great day !!!

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How do you fix the idle on a 1990 isuzu trooper 4 cylinder, and where is the adjustment?


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yes here is the common problem

Here is the most common cause of surges and stalls and low idle rough idle, it is the idle speed control air-bypass valve and throttle valve (IAC for short), they get full of gunk over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

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the only thing that can change your idle speed that much is the the isv idle speed valve u have a faulty valve or your computer is faulty

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