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High Idle, Low Tach Reading

Discussion in '1st Gen. Tacomas (1995-2004)' started by SCRunner12, Sep 30, 2017.

  1. Sep 30, 2017 at 11:01 PM
    #1
    SCRunner12

    SCRunner12 [OP] Tundra Troll

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    Robert
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    So I'm looking for some insight into my issue of a high idle and a low tach reading. Right now my 3.4 auto (99 4runner but same set up as Tacoma) starts at a normal idle, but after a short drive the RPM's jump up high (maybe 1600-2000). Only problem is the tach reads lower than the actual RPM's. It will often read around 900 RPM, but the engine is running around 1600-2000. Also it will read at 0 RPM when sitting in gear. Just took a drive and it was 500 RPM when I was cruising at about 40 MPH. Anyone have or had this issue?

    I’ve cleaned the throttle body, IAC and MAF tonight. Friend mentioned the crankshaft position sensor.
     
  2. Sep 30, 2017 at 11:59 PM
    #2
    Dalandser

    Dalandser ¡Me Gustan Las Tacos-mas!

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  3. Oct 1, 2017 at 12:20 AM
    #3
    mechanicjon

    mechanicjon They call me "Jonny Stubs"

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    I'd have to do a little research on the electrical circuit gor tach. I'm outta town and not near my PC.
    Wont be home until Tuesday.
     
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  4. Oct 1, 2017 at 1:22 PM
    #4
    cruisedon66

    cruisedon66 Well-Known Member

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    Just a guess. Clean engine grounds. Sounds like tach itself is failing. If you have digital odometer,
    check the accuracy. Maybe the circuit board is failing?
     
  5. Oct 2, 2017 at 10:27 PM
    #5
    mechanicjon

    mechanicjon They call me "Jonny Stubs"

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    The tach gets its signal from the ignition igniter. The book says check for proper voltage to tach. If it has volts and is not accurate change tach.
     
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