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Do the vacuum test outlined in the TSB, that's the only way to know for sure. Also take a vacuum reading at the intake with the engine running just to make sure it's up in the 20-22 range. If it's not the intake manifold gasket could be leaking at one or more of the intake ports.
Is the 20-20 while holding steady at 1500-2000 rpm or at idle?
Thanks!
My vacuum shows 16.5 at idle though no twitter talk mods, lol... Also, this old engine is still eating up about a qt. of oil every 1k or so, The plenum job will be in the near future, just need ambition and time