Vacuum Leak or Unmetered Air?

usafa · usafa's Garage

I have my IC and blow-off valve body off my 88 930 and noticed an open threaded bolt hole in the bottom of my intake manifold when I looked down into the throttle body. It is about 3 to 4 mm in size. This is open to the outside as I can shine a light from behind the manifold and air metering body and can see the light from inside the throttle body through the hole. Isn't this a source for unmetered (and dirty) air to get sucked right into my cylinders through the intake manifold? Check out the photo.

If you look at the photo you will notice a bolt protruding up about 1 in. away from the open hole. I can't tell what should be attached here if anything. Should this hole at least be plugged? Can't get to underside of manifold without completely removing it or the air metering body?

Help?

dean · 01-19-2003, 01:31 PM

Huh, That does seem right now does it. So if you shoot carb cleaner down there it would hit the fan shroud? That would certainly be a vacume leak and unmeater air getting into your motor. Not to mention a small boost leak. I don't know what goes there but I would find out. Sorry not much help here

usafa · usafa's Garage

Blown,

I just got off the phone with the mech who modded my engine and I have an answer to the mystery. Apparently, there was an "air flow divider plate" that he fabbed and installed at that location. The flow plate is supposed to divide the air flow more evenly or possibly to increase flow to both sides of the intake manifold resulting in a HP boost. The plate had bolt holes that were threaded and apparently at least one of the bolts backed out and the other one let go for some reason (he used loctite) resulting in the divider plate letting loose and sliding somewhere inside the manifold which is where it is now.

I understand the plate is too big to fall into the intake ports, but it may be now hindering air flow to one bank of cylinders. Now I just have to figure out how to get that thing out and decide if I want to reinstall or not!

Now maybe THAT was the reason I suddenly started having cold idle issues and intermittant warm idle issues just recently!

HOLY BLOCKED INTAKE RUNNERS BATMAN!!

dean · 01-19-2003, 05:18 PM

Maybe you should not go to that mech anymore.

stomachmonkey · 01-19-2003, 05:30 PM

If you can get the piece out I personally would not put it back.

Regards,
Scott

usafa · usafa's Garage

Dean: The mech is in another state so the car will probably not see him again anyway. He did the engine top end and mods for the PO. In his defense he has taken the time to talk to me about the history of the car as he knows it, about the mods he did, and how to set it up correctly.

Scott: I think you are correct. I may try it without. I will have to repair/plug the bolt holes though.

Any recs on what kind of high temp epoxy I could use? I guess the only reservation I have about that is if the epoxy plugs come out, down the intake they go.

Other options are:

1. Remove the intake manifold, tap the bolt holes and install short bolts w/loctite from the bottom. The bolts would be just long enough to fill the holes but not protrude into the intake. More work but a better fix?

2. Buy a new/used stock intake manifold

3. Buy a performance intake (is there such a thing?)

Why am I NEVER happy with the HP I've already got?

dean · 01-19-2003, 07:31 PM

I would almost never put something in the intake that could come loose.

If you can get at the bottom of the intake then you could put bolts in from the bottom. The holes must be tapped already.

usafa · usafa's Garage

Dean,

The mech said the holes in the intake itself were not tapped when he did the work. It looks like I'm about to learn how to pull an intake manifold off a 930.

Must have books and pics first though, so I will begin ordering a few of the recommended manuals and read up prior to tearing into it.

usafa · usafa's Garage

That tiny hole seemed like such a little thing though.....

usafa · usafa's Garage

Bump.

Not really. I have considered on this thread replacing the intake manifold. However, the one I have has been ported to 36mm along with my heads and flowed by Extrude Hone so I believe the best course of action is to remove and repair the manifold at this time.

Once the $$$ become available then full rebuild with twin plug, efi, p/c, ect will definitely be in the works!

Maybe Next Year...sigh