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1989 Chevy K5 Blazer uneven idle

I have an '89 Chevy K5 (fullsize) Blazer that was sitting for several years. I did run it for a short time once or twice each year. It has all of 43,000 miles on it. It is a 5.7L (350), auto trans, A/C, with California emissions.

It is buring way to rich and "hunts" in rpm in idle, and to a lesser degree when at hight RPM. It does not hesitate when the gas pedal is pushed.

I have had the injectors changed, the Thottle body rebuilt, the O2 sesnor changed, the T-stat changed, Idle Air Control valved changed, spark plugs, wires, distributor cap and rotor changed, fuel filter changed. The timing has been set (TDC). I have not yet verified fuel pressure as I didn't have the right fittings.

I have done a visual check of the vacuum lines, no obvious cracks, althought they are all old and could be replaced. The next step suggested is to replace the intake gaskets. Thought being if air is leaking by, the system may "think" it needs more fuel to make up for the increased air.

Can't help but think I'm missing something easy.

Any help is appreciated.

Goin' nowhere in North Pole, AK

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  • kruncher Dec 10, 2008


  • kruncher Dec 10, 2008

    The fuel is a concern. I added quite a bit of fresh fuel and it's almost all gone, so I hope that between fresh fuel and the new filter that is mitigated. We sprayed around the intake with WD-40 rather than carb cleaner. I'll check the EGR as I've not thought of that.

    Got a line on the proper fuel line fittings for the pressure test so we'll get that done too.

    I understand that the spring in the fuel pressure regulator inside the TB is a common problem with this engine. I'll have to make sure it's within specs as well.




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I had this probelm, we found that the throttle body gasket was letting air in through a tiny pin hole, new gasket fixed it. You have rebuilt yours, maybe check the seal. Be sure and use a new gasket.

Posted on Jan 24, 2009

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It is almost impossible to guess the right thing. Need to have someone scan data and see what the computer is seeing. have you taken a fuel sample?is gas old? to check for vacuum leaks you can spray carb cleaner around intake and listen for rpm changes this must be done with engine cool to keep from catching fire. also check your egr valve and see if it is opening at idle

Posted on Dec 09, 2008

  • TripleTauto
    TripleTauto Dec 10, 2008

    check your map sensor also be sure it has good vacuum source



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