Does it affect the performance for better or worse if you do not install one of these valves? I have a slight hesitation from a stop on acceleration and wonder if this could be an issue. I do not have one but could get one at a junkyard if necessary. Thanks for you help! It's for my 1974 350 BTW.

 

Brenda, I think you're talking bout the one at front of engine, between intake and water pump? That ties into EGR and a wacky EGR can definitely cause that hesitation. My solution is to plug the EGR vacuum line at the EGR valve and disable it.