Zip-tied tube under 4.0 SOHC upper intake - What purpose does this serve?

Hi Folks,

Am almost finished with the '97 SOHC repair and have yet another question for you. On the underside of the upper intake manifold, there's a black plastic tube that's tie-wrapped to the intake and connects to a oddly shaped tee (likely unavailable or really pricey to replace). Does anyone know what it's purpose is? It reminds me of a "water shock/hammer absorber/damper/arrester" used in plumbing.

The reason I ask is because my "tee" was ripped so I did not reinstall it. Instead, I bypassed it and ran a 3/4" 90-degree elbow from the IAC valve to the plastic line that runs over toward the passenger-side front near the air box. Am hoping it won't really matter, but don't really know. As always, any info is sincerely appreciated. TIA.

--mike

Hey Mike I have a similar tube on the driver's side under the upper intake manifold. Mine is tied up with string not zip tied.
I would love to find out it's purpose.

Is that the vacuum reservoir for the Variable Intake System? Or maybe just a general purpose reservoir.

VIS vacuum reservoir

That is not the VIS vacuum reservoir. It is located on the passenger side.

The "tuning tube" was not present on my 2000 SOHC upper intake manifold. I suspect it was eliminated in 1999 along with VIS. Because of that, I have advised several members to eliminate it rather than pay the exorbitant price for the assembly when the elbow fails. To my knowledge no member has reported anything negative after deleting it.

2000StreetRod said:

That is not the VIS vacuum reservoir. It is located on the passenger side.
View attachment 79927
The "tuning tube" was not present on my 2000 SOHC upper intake manifold. I suspect it was eliminated in 1999 along with VIS. Because of that, I have advised several members to eliminate it rather than pay the exorbitant price for the assembly when the elbow fails. To my knowledge no member has reported anything negative after deleting it.

Click to expand...

Really appreciate everyone's info and advice here. I finally got this thing running and can also attest to the fact that the absence of this tube does not seem to make any difference at all. Although, when I first started it, the CEL was on and it wouldn't idle worth a darn and kept dying, which really made me wonder about this tube. Turned out to be a failed IAC valve. After replacing it, it runs great and idles smooth and there are no knocks, clicks, rattles or other noises coming from the engine. I'm really happy that this turned out so well, especially after having to replace all 4,862 ;-) timing chains, gears, guides, tensioners and spending a fortune on tools and "criminally overpriced" gaskets.

All in all, it's been a very educational "repair adventure". Now I can resume knocking out some of less dramatic repairs and hopefully get on with life.

Did anyone ever figure out what the point of this tube is in a way that makes it undesirable to remove altogether?

I've just had that T-connector repaired in the same way as described in the cheap easy hose fix thread here ...

Air inlet hose fix?

Truck seems to run fine without the extra tube ... so far.

There's something similar on my 2003 4.6L V8 that's referred to in the shop manual as a resonator.

I think the purpose of these air chambers is to reduce air intake noise at engine idle speeds.