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OT: Pontiac engine problem

Discussion in 'Off Topic Threads' started by len loma, Aug 6, 2009.

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  1. len loma

    len loma TS Member

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    Jan 29, 1998
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    Have A 99 Grand Prix which is now my work/weekend shooting transportation. The 3.8 liter V6 engine has 152K on it. Does not burn oil and starts fine. When warmed up fully it idles rough to the point it feels like it is loading up engine with excessive fuel. High ways speeds it is fine. Looked for vacuum leaks but can't find any. Any ideas of what it could be? thank you
     
  2. Milkbone

    Milkbone TS Member

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    3 words for you: CASH FOR CLUNKERS

    Sorry, I couldn't resist.
     
  3. trapshootingfran

    trapshootingfran TS Member

    Joined:
    Jan 29, 1998
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    When was the last time the O2 senser was changed? when at idle the enging runs in what is known as open loop if the O2 senser is not reading the proper temp. When @55mph it goes into closed loop, and it runs fine. You also could have a weak injector. You need to change them once in a while.
    Only a guess I'm not there. Good luck Fran
     
  4. AveragEd

    AveragEd Well-Known Member

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    Jan 29, 1998
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    Location:
    Mechanicsburg, Pennsylvania
    If the cover over the top of the engine says it is a Series II engine, pull the EGR valve out and inspect the inside of its cavity. Those intake plenums are known for burning through in that area. The last I knew, replacement plenums were about $150 including gaskets; be cautious buying used ones as you may get one with the same problem or about to have it.

    A failed sensor almost always triggers the "Service Engine Soon" light but an intake plenum problem often doesn't.

    Ed
     
  5. Lead Man

    Lead Man TS Member

    Joined:
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    Could be the start of a mass airflow indicator problem. It happened to mine at about that mileage. I looked at the plenum and was about to have the same problem as mentioned above. I now have over 200k on it.
     
  6. len loma

    len loma TS Member

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    Jan 29, 1998
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    When it loads up sometimes the "service engine soon light" comes on and eventually turns off after driving highway speeds for a while. It would be worth looking at mass air flow sensor and O2 sensors. I wonder if this would be a fault code that would be stored if scanned? I did hear about the plenum problem and will check it out also.

    I bought it new and it has had very minor problems pop up. This being the biggest. The dam thing still gets 23mpg yet and when running right gets up and goes.

    thanks much
     
  7. Quack Shot

    Quack Shot Active Member

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    I'd also add the intake manifold to the checklist. If you can get the codes from the processor, they can give you a better idea of what's going on. Even better would be to use a scan tool and look at the fuel strategy parameters.
     
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