Idle Issue; not a very unique title I know

[willincalgary]

Thanks for your help everybody. As you may know I'm traveling around the western US in my truck right now sampling rocks for my research.
In a fit of utter desperation I dumped literally an eighth of a can of carb cleaner on the number 3-4 intake manifold. I just couldn't believe that the symptoms weren't caused by a vacuum leak. Well this time the engine nearly stalled and I nearly cried. I guess the liberal sprays that I used in the past were insufficient. Amazing because 3 people, including me, sprayed various products around the engine looking for a vacuum leak and decided there wasn't one. I suspect that the leak is on the lower side of the Manifold and unless you really soaked the manifold the fluid vaporized before reaching the leak and affecting the idle. I literally soaked the manifold in liquid.
So the good thing is I found a vacuum leak. The bad thing is I don't have a manifold gasket with me. Can one be cut from some material, much as you would do with any other gasket? I would imagine it needs to be a high temperature material due to the exhaust.
Thanks again for your help.

[willincalgary]

I just remembered I have the metal intake manifold gaskets that come in the head overhaul gasket set from our hosts. Perhaps I will reuse the fibre gasket and add the metal gaskets to the intake portion?

[Tim Smith]

If it's an intake leak, you can also test with soapy water. Spray liberally and look for the idle to raise. Once it does that means you have enriched the mix by closing off the air leak. Focus on that area until you can identify it. Kind of basic but it's pretty fool proof and you can spray the whole engine down with little risk of fire that way.

I think you might have a sticky valve which could be due to the rocker assembly or maybe even the rollers if not (obviously) the valves. Not a big deal if performance is not effecting you too much.

The easiest way to find a sticky valve is with a piece of paper. Hold the paper over the exhaust outlet and see if the paper gets sucked in on the failed fire. If it does then you have a bad exhaust valve. You can do the reverse for the intake valves. Hold the paper just close enough and wait for it to blow away. If it does then you have a bad intake valve.

You say you're on the road right now. So it is too tough to do a tear down. In that case, you might get lucky with a Marvel Mystery Oil run in. That or ATF. Simply get the engine up to hot working temps. Pull the vacuum line from the distributor and insert it into your can of MMO or AFT. In fact a glass of water will work too but only if the engine is really good and hot. Once the tube is inserted in your jar of... whatever, rev the pis out of it, going from idle to full open and back. Do not try to do it quickly by dumping fluids down the carb unless you have a good hand for healthy vs hydraulic. Be very careful to only chose the vacuum line from the distributor. Smoke will happen out the exhaust too.

If done correctly, you will hopefully be able to steam off the carbon that is in your top end and clean off the valve seat (or in many cases the stem). This is only if you are lucky though.

I'm sure that after all this, you find a spark plug lead that was loose which will fix the the whole thing. Either way, I hope you make out alright.