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Thread: 1999 STS vaccum leak?

  1. #1
    jaybee86 is offline Cadillac Owners Member
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    1999 STS vaccum leak?

    Ok so this morning start the car I here a hiss from under hood and when I got off hwy it started to really rough idle at lights but fine while its rolling on hwy does that sound like hose or sumthing worse


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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: vaccum leak?

    Have you opened the hood and snooped around? Tried to pin point the sound? Looked for broken or loose vacuum lines?

  4. #3
    vincentm's Avatar
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    Re: vaccum leak?

    Check the PCV valve elbows on both heads and ends.

    PURPOSE
    A Positive Crankcase Ventilation (PCV) system is used to prevent blow-by gases from escaping to the atmosphere by routing them through a vacuum controlled ventilation valve, into the intake manifold. Fresh air from the air cleaner is pulled into the crankcase, mixed with blow-by gases and then combined with the air/fuel mixture and are burned in the combustion chamber.

    OPERATION
    The primary control is through the PCV valve which meters the flow at a rate dependent upon manifold vacuum. To maintain idle quality, the PCV valve restricts the flow when intake manifold vacuum is high. If abnormal operating conditions arise, the system is designed to allow excessive amounts of blow-by gases to back flow through the crankcase vent tube into the air cleaner to be consumed by normal combustion.

    SYSTEM FAULTS
    A plugged PCV valve or hose may cause:
    • Rough idle.
    • Stalling or slow idle speed.
    • Oil leaks.
    • Oil in air cleaner.
    • Sludge in engine.
    A leaking valve or hose could cause:
    • Rough idle.
    • Stalling.
    • Erratic idle speed
    Attached Images

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    jaybee86 is offline Cadillac Owners Member
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    Re: vaccum leak?

    I have and its coming from passenger side of engine but just can't tell exactly but hiss sound is towards fire wall. Are the vacuum hose big or small I'm not a car person like that so help plz

  6. #5
    vincentm's Avatar
    vincentm is offline Cadillac Owners Connoisseur
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    Open the hood, stand on the passenger side, and look on the rear corner of the engine next to the coil packs. Removing the Northstar Engine beauty cover will help a lot.

    The elbows on these tend to crack some times

  7. #6
    jaybee86 is offline Cadillac Owners Member
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    Re: vaccum leak?

    Ok found problem hose but don't kno wat the hell to call it

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    jaybee86 is offline Cadillac Owners Member
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    Re: vaccum leak?

    This is a pic of the hose I believe Vincentm was talking bout

    IMAG0278.jpg

  9. #8
    vincentm's Avatar
    vincentm is offline Cadillac Owners Connoisseur
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    Thats it, inspect both of them closely

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    jaybee86 is offline Cadillac Owners Member
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    Re: vaccum leak?

    This one broke completely when I touched it but what is this hose called n while I'm here do I need to change others or as they go?

    And is that metal part that come out with hose a sensor I need to replace or I just need hose

  11. #10
    vincentm's Avatar
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    The PCV tube/hose. Take it to an oreilly or napa and get it replaced, elbows too

  12. #11
    jaybee86 is offline Cadillac Owners Member
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    Re: vaccum leak?

    Thanks you guys are the best ppl to have!

  13. #12
    vincentm's Avatar
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    Quote Originally Posted by jaybee86 View Post
    And is that metal part that come out with hose a sensor I need to replace or I just need hose
    The metal part is the pcv valve itself.

  14. #13
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    Re: vaccum leak?

    It's the dirty air PCV vacuum line. It can be replaced with a length of proper ID reinforced rubber fuel hose. Have fun attaching it to the passenger end of the intake manifold. Check your PCV rattle valve, too - if it doesn't rattle, replace it ($2.50). FWIW, the 2000 and later engines do not have a rattle valve - it's a fixed orifice. No !

  15. #14
    jaybee86 is offline Cadillac Owners Member
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    Re: 1999 STS vaccum leak?

    Is there a certain way to get obvious valve back in?

  16. #15
    Submariner409's Avatar
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    Re: 1999 STS vaccum leak?

    The rattle valve has a large and small diameter. The large smooth end sticks into the cam cover grommet, the dirty air PCV line slips over the small end with retainer hump.

    Air flows through a PCV valve only one way: FROM the engine (cam cover) INTO the intake manifold.

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