groho

Is it possible for the spring tension on a PCV valve to be too strong for the manifold vacuum to overcome at idle? Essentially creating a controlled vacuum leak.

Have a strong 289, 66 coupe, pulling 19 PSI manifold vacuum at idle, spec is >18 PSI. PCV valve is the properFRAM FV156. When I check the PCV valve it appears the poppet is not seating up in the PCV socket at idle, either because the weight is too heavy or the spring tension is too strong. When I block the PCV with my thumb, idle smooths out real nice and idle speed drops about 100+ RPM. All hardware and hoses are new. Comparedthe PCV tension with other V8 PCV valves, GM, Chevy, Ford, etc, and this FV156 is noticably stronger/stiffer. Any suggestions? Any way to determine the minimum vacuum for a particular PCV or is it strickly hit and miss?

falconfixer

Try the $1.99 solution and swap with a new one (if you have not already)...

No, excess vacuum is not the issue. And there may be another vacuum leak or carb idle/rich setting issue that this masks.

jlg2002

They "leak" at idle too. If the one you have is causing the engine to run rough, replace it. If that does not help , then you are too lean at idle to start with.