Vacuum leak at throttle body air intake- 1996 GMC Sierra c1500 4.3

[chriscg]

Hi. Im new here. so hello! My name is Chris

im getting a vacuum leak where the air box eventually connects onto the throttle body. I think its a vacuum leak because I am able to coast at 20mph for about 6 or so seconds without my foot on the throttle and the revs stay raised a bit ( its like my foot is gently on the gas) Im also getting some surging after I first take off and then let my foot off the gas.

Anyway, Iv sprayed carb cleaner at this location and can tell a big difference in engine speed for sure. The thumbscrew holding the intake onto the throttle body was lost a long time ago. For some reason I cant grab any threads on the stud that the thumb screw goes onto with a normal bolt? The studs threads don't start until about a quarter inch down, if that makes any sense? I was able to loosen the actual stud a bit to get a bolt on and tighten it down a bit but im sure that is not good at all.

I think my main issue is the a plastic seal/gasket inside the air intake that sits on top of the throttle body and goes over/onto the throttle body itself. Its cracked into two pieces and old. I am sure this is letting in air causing my issues. I can not find the name of this seal or part number that I need to replace. Iv looked everywhere online and cant find it either. Is there any other way to seal this part of the intake otherwise? Remember, I'm not talking about the throttle body gasket. I'm talking above that, at the very top of the throttle body where plastic and metal meet. Its almost like there shouldn't even be one there, but it is?

I'm sorry if that doesn't make much sense. Its a hard issue to describe. I'm not the smartest at identifying parts either.

Here is a picture of the place I'm talking about. The red line is where the gasket is and my leak is. Any advice would be greatly help!

 

[GoToGuy]

That area is before the throttle body venturi, regulated controlled airflow. You can run without the airbox and silencer. Before the throttle body is a fixed, static area. It does react like an, after the venturi vaccum leak. Good luck

 

[chriscg]

Sorry but I'm not that technical at names. I haven't worked on many cars but this truck and some older vehicles. Iv done allmost all the work on this truck in the past decade though.

Can you simplify that just a little? Are you saying I can run without the air box, air intake temp sensor, and mass airflow? Or are you saying I can take off the silencer air box and run straight the the throttle body from my air box?

What is a fixed static area?

And are you saying my symptoms are like a vacume leak where I circled?

Thank you.

 

[evilunclegrimace]

You do not have a vacuum leak. You have a leak in the air intake duct work, two different animals.

 

[1998_K1500_Sub]

You do not have a vacuum leak. You have a leak in the air intake duct work, two different animals.

The leak, as the OP believes it to be, is downstream from the MAF sensor (it's a 1996) and just prior to the throttle blades. If it's significant he may have a drivability issue on that account of the MAF being bypassed by the leakage flow.

 

[alpinecrick]

The leak, as the OP believes it to be, is downstream from the MAF sensor (it's a 1996) and just prior to the throttle blades. If it's significant he may have a drivability issue on that account of the MAF being bypassed by the leakage flow.

This^^^

Problem is, I don’t know what the name of that danged gasket is or where to find one. I got lucky and had laying around big o-ring that fits around the Venturi intake perfectly.
With your VIN the dealer can find it on their schematics.

 

[alpinecrick]

I think it called a throttle body seal or air cleaner seal. The parts store may be a good bet. Measure across the throttle body and head to the parts store with your tape measure in hand. There are probably a bunch of these for different applications that are the same size. Even the TBI motors may have the same seal for the throttle body.

 

[df2x4]

This discussion has come up a few times here over the years. Unfortunately I don't think GM ever sold that seal by itself as a replacement part. It just comes with the throttle body hat. If you want a factory part you'll probably have to just pull a different one from a salvage yard, as it looks like the hats are now discontinued.

Here's a diagram for the 5.0/5.7L Vortec intake, notice there's no listing for that seal.

https://www.wholesalegmpartsonline....odel=14486&modelYear=1997&ukey_category=19400

If that seal ever was available separately, @MrPink would be the one to know.

 

[chriscg]

The leak, as the OP believes it to be, is downstream from the MAF sensor (it's a 1996) and just prior to the throttle blades. If it's significant he may have a drivability issue on that account of the MAF being bypassed by the leakage flow.

This is correct. Thank you for clearing that up and also giving me a better way to describe where my issue is at the same time.

I think it called a throttle body seal or air cleaner seal. The parts store may be a good bet. Measure across the throttle body and head to the parts store with your tape measure in hand. There are probably a bunch of these for different applications that are the same size. Even the TBI motors may have the same seal for the throttle body.

I will definitely try the parts store with those names. I don't think iv asked for an air cleaner seal before, but that makes total sense. Ahh! I can't belive I didn't even think about measuring it myself! That would help a bunch lol.. Actually, I was wondering the same thing about the TBI engines seal. Iv seen those in the parts store. Il probably measure like you said and see.

Thanks for the help people. I shall continue to look for this alusive part!

 

[xXxPARAGONxXx]

You won't find that part. It’s not very practical to search a junkyard for another air cleaner part just in order to have a replacement sealing ring. Eventually, all the sealing rings will be gone, and we will all need to come up with a practical solution.

What I did (and another member did, before me) as a fix seems to be working.

Resonator air box gasket

The O ring from the upper manifold that seals the spider is what I used. It took a bit of manipulation but it seals now. That is what I decided to do as well. I placed it around the opening, held it down using the cap to a MAF sensor that I had on hand, then "tacked welded" it in place with...

www.gmt400.com

Super Glue does not seem to adhere well if affixed only to the O-ring. Make sure you affix the Super Glue to both the metal of the throttle body and then the O-ring. Do not affix Super Glue between O-rings to make the O-rings adhere to each other. The Super Glue needs at least one anchor onto the metal. Use two O-rings. Make sure you clean any oil residue from the O-rings using alcohol.