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Need Advice: 89 Truck Idle Problem

Discussion in '95-older Toyota Truck Tech' started by NMC_EXP, Jan 1, 2018.

  1. NMC_EXP

    NMC_EXP

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    I have an '89 Toyota truck, 3.0L, auto trans, 4WD. The truck has 147K miles. Baseline tune up by a Toyota dealer when I bought it at 101K miles.

    Truck was starting and running fine. Problem came on all at once:
    -- Cold engine starts fast and easy (outside temp from 30 to 60 degrees).
    --But when it drops down off fast idle it stumbles and misses hard.
    --Seems to run alright when driving and once it warms up the idle mostly smooths out.
    --Now when the engine is warm I have to crank it a long time to get it to fire and start. Used to fire right off.

    Any suggestions on where to look first will be appreciated. I'm dumber than a box of rocks when it comes to engines newer than about 1965.
     
  2. ntsqd

    ntsqd technerd

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    Could be a vacuum leak. Usual detection methods apply. There's a slotted head "screw" in the side of the throttle body, mine leaked there. Also had a split in the air hose going to the throttle body that was throwing off things, not to mention leaking dirty air.
     
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  3. NMC_EXP

    NMC_EXP

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    This came on all at once. Vacuum leak makes sense.

    Thanks
     
  4. NMC_EXP

    NMC_EXP

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    This is strange. Had this problem for 3 weeks, not intermittent - 100% malfunction.

    The battery has been weak for quite a while. Yesterday it would barely crank so I put a new battery in it. While doing that I pulled the air filter to check condition - was not too bad and I reinstalled the used filter.

    Here is the strange part - after installing the new battery and R&R the air filter housing lid, the truck is running perfect again - idles smooth, fires right off when warm, no rotten egg smell.

    Is it possible that at idle speed a very weak battery could have screwed up the ignition or fuel injection?
     
  5. ntsqd

    ntsqd technerd

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    Check or have your alternator checked against the specs for it.
     
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  6. NMC_EXP

    NMC_EXP

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    Will do. Seemed to me the alternator ought to be able to handle ignition and fuel with no battery.

    Thanks
     
  7. ntsqd

    ntsqd technerd

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    I thought so too, but recently went thru this on a '73 GM truck.
     
  8. NMC_EXP

    NMC_EXP

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    Near dead battery messing with engine performance?
     
  9. ntsqd

    ntsqd technerd

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    Battery not being fully charged messing with starting performance. Cranking voltage was in the green zone, but it couldn't supply the amps needed for the IGN to work while also turning over the starter. GM HEI's are known power hogs anyway.
     
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