[Tomnavigator]

I am in the process of carbon cleaning my 335D with 90,000 miles. I found a wonderfully easy way to find out which cylinders have the intake valves open and which have the intake valves closed.
First the hard way using a bore scope:
I tried a bore scope camera and had the usual problems of gunk coating the lens. Then getting it around the bend in the intake to see the valves. Then focusing problems and lighting problems. I finally determined all cylinders had closed intake valves except cylinder 6. I still was not sure if any intake valves could be just cracked a little. This method took 15 to 20 minutes and still left me wondering if a valve might be slightly open.

Now the easy way:
I put a small piece of toilet paper just large enough to cover the port over one port (I used the round one) and got an air hose and blew into the rectangle port for the same cylinder. If the intake valves are closed, the toilet paper stays put and does not move. I did this for all cylinders and when I blew air in cylinder 6, the toilet paper took off like a rocket. This method took maybe two minutes at the most to do all cylinders twice. There is no doubt in my mind that cylinder 6 intake valves are open. The toilet paper never wiggled on any cylinder but #6. I am convinced cylinders 1 thru 5 are closed.

The air goes in and if the intake valve is closed, the air has nowhere to go. If the intake valves are open, the air goes into the cylinder then back out the other intake valve and up the port to blow off the kleenex.
Easy Fast, No Doubt.

I did not try to seal up the air line. I just pointed my blow gun down the rectangle port and blew. I bet it would work using a shop vac with the hose reversed to blow air instead of sucking air.
PS: I would not use a vacuum on suck because the kleenex would be sucked into the cylinder and probably not ever come back out.

I used two ply toilet paper and removed one ply to keep the weight down do it would fly easier. I tore it so it covered the port completely without being too big. I used the same piece repeatedly so only one piece is needed. I used a standard air gun on an air hose and just pointed the end down the port. You could seal it some for more dramatic results but I don't think it is needed. Other possible air sources could be.
Canned air for cleaning a computer, leaf blower, vacuum hose set to blow out instead of suck, hair dryer. Everyone has to have one or more of these. Super easy and super quick. Results obvious.