If you can mechanically open the valve with the engine running it should stumble with the big vacuum leak created. There is a tube from the valve around the back of the head to the bottom of the intake that clogs, if no stumbling that tube is clogged. Replace it with new if possible first, second is to try to clean it out with an old speedometer cable...not fun.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer