SubwayVQ

So I just got done pulling off my upper intake plenum to re-torque my rear spark plugs, and everything went fine. Car started and runs good. However, I can now hear what sounds like a vacuum leak. It’s a hissing sound. I sprayed brake cleaner around all the hoses I removed, but the idle never changed.

One thing that did happen though is I snapped off the bolt that holds the rear O2 sensor bracket to the back of the intake. The head snapped off and it’s cross threaded in the back of the intake now. I don’t know if that bolt can cause a vacuum leak, but I was gonna put some JB-Weld over it to seal any leaks possible. Does anyone have any other suggestions?

maximatech12

Hissing is normal its your aux air in the T.B.

Hit the throttle manually a few times you'll hear it as the plate opens.

SubwayVQ

Sorry, I forgot to mention it's a 2002 with the 3.5

If I can't sort it out by the end of the weekend, I'm gonna say screw it and just drive it. I drove it already and haven't noticed anything to raise concerns.

maximatech12

It doesn't make a difference what year
When the car is at idle it sucks air into the plenum. It passes through a small opening usually in the T.B. causing a hissing noise.

cornholio

iTrader: (1)

are you suggesting a noise he did not previously hear has been there all along?

maximatech12

OK he's got a leak then?
Well he checked everything with BP cleaner!
Maybe he cleaned the Throttle so well and its.like a whistle Now?
I have this noise too and rebuilt the whole throttle area and it's in the throttle.

SubwayVQ

I didn't clean anything, only pulled the upper plenum off to tighten the rear plugs and then slapped it all back together. The hissing is definitely coming from the back where that bolt snapped. I'm gonna try putting JB-Weld over it and see if it fixes it.

Donkeypunch

are you talking about the suction noise when you open the throttle real fast?

maximatech12

Yeah that's what I figured he was hearing but also the Ivt/iacv noise.
This member had a similar issue.
Cracked intake plenum - Maxima Forums
https://maxima.org/forums/5th-generation-maxima-2000-2003/695708-cracked-intake-plenum.html

DennisMik

iTrader: (2)

He probably has a vacuum hose that got pulled off or broke that he didn't realize and as such didn't do the spray in the correct spot.

Derrick2k2SE

iTrader: (3)

If the broken bolt were causing the leak you could put your finger over it and stop the leak. Those mount bolts don't go all the way through.

A vacuum leak will be a steady hiss at idle. It will tend to go away when the throttle is opened as that reduces vacuum.

SubwayVQ

I put my finger over it and did not feel anything or stop the hissing. I'm really stumped on this. It is definitely coming from the same area, but I sprayed everything over there with brake clean. PCV hose, hose connecting both VC's, brake booster hose, block off plate, elbow gasket, TB gasket, plenum gasket, and still nothing.

It may have been there the whole time and I never payed attention until now? I don't know, but the car is not running anymore rich/lean than it was before, so I don't think it's a huge deal.

Derrick2k2SE

iTrader: (3)

The noise may have always been there. It's different when you actively listen with the hood open. If it's a leak you can hear there would probably be a rough idle.