Intake manifold leak - how common are they?

1 2 3 Next
  • #1

    Intake manifold leak - how common are they?

    Finally got my z31 turbo on the road again, although I notice if I rev the engine, I can hear air 'wooshing' right after I start to give it throttle (I do this with the control on the throttle body; easier than in cab) when its hot or cold. The idle is kinda rough, and it does miss a bit while idling. It runs fine while driving, and if I drive around for a bit and stop to idle, it seems to be fine after a bit of driving.

    I can hear the air 'wooshing' beside the throttle; close to the back of the intake manifold… is that a common area to 'leak'? Does this even sound like it could be a manifold leak?

    (Ill try to get a video later, too, btw).
  • #2
    Check your throttle shaft.
  • #3
    Robyr wrote: Check your throttle shaft.
    Im not too sure I know what that is. :/
  • #4
    maverickxeo wrote: Finally got my z31 turbo on the road again, although I notice if I rev the engine, I can hear air 'wooshing' right after I start to give it throttle (I do this with the control on the throttle body; easier than in cab) when its hot or cold. The idle is kinda rough, and it does miss a bit while idling. It runs fine while driving, and if I drive around for a bit and stop to idle, it seems to be fine after a bit of driving.

    I can hear the air 'wooshing' beside the throttle; close to the back of the intake manifold… is that a common area to 'leak'? Does this even sound like it could be a manifold leak?

    (Ill try to get a video later, too, btw).
    Check the hose that goes to your brake booster.

    Look at the manifold where it connects. Look right under that hose, and you'll see a smaller hose. Look under your throttle body and look at the small vacuum lines going there too. There are some tiny fittings there that may need some capping.

    Look at all your vacuum lines and just work back to the manifold and inspect around the ends for cracks.
  • #5
    I did a quick look around the intake throttle body and manifold… didnt see anything unusual.

    Ill check tommorow/get a video when I can run it (Its pretty late here haha).
  • #6
    I have the EXACT same problem. Sometimes I have vacuum leak starts where it's lean as hell and I have to hold the pedal down to give it gas while it warms up. Also I'm running SUPER rich driving around. Idle is fine though once at operating temp. I actually have it in the shop and they're hooking it up to a vacuum leak tester. I'll let you know what they tell me.
    Usual Z31 suspect: Garage Queen (aka broken)
  • #7
    I have the same air wooshing noise at just above idle. I don't know what it is.
  • #8
    You all need to inspect the throttle shaft seal. Spray some starter fluid around it.
  • #9
    I'm willing to bet the throttle-shaft seal is bad. Mine is as I discovered in a recent boost leak test. I'm not sure how to fix it barring rebuilding the TB. May just look for another TB. Also, pinch some vac lines shut when you hear the noise and see if it stops. I have one vac line that makes a hissing noise only when the throttle is cracked; I found it by pinching it shut and the noise stopped.
    "When you approach the world with the apron of a servant, you're allowed to go places you can't if you approach it with the crown of a king."~Jon Foreman
    86 NA2T. Remanufactured NA engine. T3, intercooled, 13 lb boost. 3" turbo back CM exhaust w/cat, DXD Stage II clutch, blow-through w/ BOV, E-fans, short shifter.
  • #10
    screamingflea wrote: I'm willing to bet the throttle-shaft seal is bad. Mine is as I discovered in a recent boost leak test. I'm not sure how to fix it barring rebuilding the TB. May just look for another TB. Also, pinch some vac lines shut when you hear the noise and see if it stops. I have one vac line that makes a hissing noise only when the throttle is cracked; I found it by pinching it shut and the noise stopped.
    Yeah, rebuilding them is a pain in the ASS. And near impossible. Get a newer TB off of a 240SX or other KA24 based vehicle.
  • #11
    So if the throttle shaft is bad; you cant really repair it?
  • #12
    So stupid question;

    If the throttle seal was leaking, wouldnt the vac pump run constantly? Mine stops after a while…
  • #13
    maverickxeo wrote: So stupid question;

    If the throttle seal was leaking, wouldnt the vac pump run constantly? Mine stops after a while…
    Not really. The vacuum pump just has to pressurize the cannister.
  • #14
    [quote]Robyr wrote:
    Originally posted by maverickxeo
    So stupid question;

    If the throttle seal was leaking, wouldnt the vac pump run constantly? Mine stops after a while…
    Not really. The vacuum pump just has to pressurize the cannister.
    Ah…

    But then wouldnt I not be able to make as much boost as normal?

    (Not doubting you guys; just trying to ensure I have to fix the right thing :P)
  • #15
    I had a flat out open vacuum port and I still made 10psi. You're turbo will continue to pressurize the manifold, and reach the target pressure. You are overspooling the turbo though.
1 2 3 Next