Thanks for the video.
Unfortunately, so quiet in the cabin, can't hear the engine at idle.
We need a video of it at idle from the engine compartment..

From the cabin, it sounds actually reasonable.
I can tell from the RPMs tho that it dips to 250 RPM at ldle..

How many bolts stripped??
Are you sure they are stripped?
Or they snapped??

That is going to be a tough problem.
Probably then they stripped into the head and ate the aluminum.

I don't use a torque wrench on them.

Here is trick..
get a stud in a hole
Put two nuts on the stud. Lock the nuts together.
Lower nut of the two wedged nuts- put a wrench on it.
hold the wrench in your favored hand. I am right handed.
Put the torque wrench on the top of the bolt

Feel the turque on your hand until the torque wrench clicks.
Then use this to get the feel of how tight to make the bolts on the manifold.

 

They are stripped because they snapped and were drilled out. I took great care (and a lot of masking tape) to be sure flakes didn't fall into the intake. Even after this happened, it ran fine for weeks before the present symptoms developed.

The two passenger side bolts snapped. As a clarification these are the long bolts that bolt the plenum onto the lower intake, not the intake bolts. One was drilled out almost successfully the other wasn't. The fist doesn't bolt all the way in but it does grab. The other wont grab at all. As I said I have a new intake ready to go in I just have to get around to doing it. That is in the cabin with my window open (and hood closed). I can try and take another video this weekend when it is cold (and I don't have work).

 

Ok so out of 12 bolts - one is out and the other is partially holding.
Not too bad.
What are the positions??

You may be totally OK.

No sense in taking that nightmare all apart again.
Hey, broke, get a vacuum gauge.
At idle draw a vacuum.
Take off that vacuum hose by the brake line in the intake.
If your vacuum is toward 0lbs or barr that's bad.

I don't have a vac gauge or I would get a number for you..

 

Get some cheap cigars from the gas station and do a smoke test. Trust me it sounds cheap but it works. the 1171,1174,0171,0174 are all going to be vac leaks. the misfires are probably related to the vac leak also. Your problem is the stripped bolts more then likely. If you want to confirm then try the steps below to smoke test at home.

1) disconnect the hose next to the brake servo on the intake. Insert something to plug the hose you removed, and connect another spare hose about 3ft long (to blow smoke into) on the same connection on the intake.

2) Disconnect the MAF and take off the air filter cover, and MAF housing off of the intake tube. Use a latex glove or something to stretch over the open end on the intake tube to create an air tight seal.

3) light up a cigar and start puffing. Blow the smoke in and look to see where it's coming out. Plug the end of the hose you are blowing the smoke in after every time to keep the smoke from escaping. You will know if you have a good seal because the glove on the intake tube will actually inflate.

hope this helps.

 

Out of 6 bolts...I think you're still getting confused with the lower intake though I'm probably doing a terrible job explaining. The intake to block/head bolts are fine; the plenum to intake bolts are the issue. The 4 long plenum bolts that are the ones I'm talking about. The 2 passenger side ones snapped and dont hold the plenum on the intake meaning the gasket wont seal so let in enough air to cause issues? (because it isn't metered?)

 

yes, thanks for the additional detail.
Well, that is good.
As you could replace the lower manifold.

There are 5 on ebay..

discovery II lower manifold | eBay

That is the easy way to go.
Don't bother screwing around with drilling and tapping.

Or
You could remove the upper.
Tap the holes for some oversized bolts and go that way.
But, it is a hack.

You need to clean this up before you go further..

Yeah, those top bolts.
Never use a torque wrench.
I just put some permatex non hardening sealer on that gasket and put it on both sides and put the plenum on.
I snug up the bolts. Then go around the pattern once - a little tighter
then twice a tad tighter.

I am sure my truck is under torque specs on those bolts - but I don't care.
As they are easy to get to.

I torque the critical head bolts. Transmission stuff.
But, the air stuff, I just go by feel. Cause it breaks...

Look at this clown on eBay.
Thing has a crack in the bolt hole...





OK, so you only have two stripped bolts.
Maybe it is worth it to get long ones and put them in.
As the parts on eBay may be hit and miss.

I would probably go the eBay route.
get a clear pic of the item before you buy it.

Or --
Could try to tap it.

Tapping is easy.
Run the tap like a screw.
In and out in and out.

Then test the new bolt

If good then put the plenum back on and you are set.

I would put a bunch of goo on the gasket in your case - as
you have issues with warp maybe and clamping force on those 6 bolts..

Still you could get a vacuum reading.
Maybe you are in spec.

Yeah, unmetered air is going to kill you.
If you have it.

But, you have 4 bolts holding it on.
and a 5th one too - somewhat.

So, you may be OK as you are.
you may have a MAF issue or O2.

If you put a live scanner on - well you have an Ultra scanner.

What goes the Bank 1 sensor 1 show?
Bank 2 sensor 1??

Are they going up and down between .1 and .9 volts with the engine running at idle - or at 1000 RPM held there for a time??

These O2's only run when they are at temperature.

 

yeah, you have a leak

p0733 - 3rd gear incorrect ratio
p0171 - bank 1 lean
p0174 - bank 2 lean
p1174
p1171
p1300
p0304 - cyl 4 misfire
p0302 - cyl 2 misfire
p0308 - cyl 8 misfire
p0306 - cyl 6 misfire

I would just fix it.
2, 4, 6 and 8 are on the passenger's side.
And you are lean.

Yeh mon.
Just deal with it.
Ebay is your friend.

 

I have a lower intake if you need it. No problems with it. PM me if needed.

 

I have one sitting on the floor of my garage, if I can get a weekend to put it in it would be going on (curse you 4 cords of wood!!!)

 

Well then you are set.
Lower intake replace.
New gasket with a lot of sealer.
Put the upper back on and done.