Where you are blocking it would stop a run-away condition, since that is the only air inlet. It must be getting enough air to idle thru leaks, and initially from the crankcase (via PCV tube). Did you block it off tightly and hold it for ~20 sec? If everything is tight it would suck the crankcase down to ~10" Hg vacuum and then stall for lack of air.

If you want to be more assured, block "B" in post 8 photo. In know that works because I once stuffed paper towels there while installing a replacement engine, then missed them when I put the plastic duct back in the dark. The car idled, but wouldn't go faster than 5 mph. I started worrying that the engine was bad (it ran fine on the ground), but measured 10" Hg vacuum on the intake which tipped me to the problem.

I did like you first time I replaced a stop valve, based on the Diesel Giant article. Since then I wonder how anybody could install a stop valve thus. You would have to jam it into the IP if it was pushing on the back of the lever. It should go in easy and the arm grab the lever when you pull it back. Pretty obvious once you do it. Just install it angling in from the block side (where there is more room anyway) and with the stem sucked in.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans