All engines are equipped with a positive crankcase emission control system. The PCV system routes a harmful mixture of blow-by gases and condensation vapors through a modulating valve and into the intake manifold where they combine with the carburetor air/fuel mixture and are burned in the combustion chamber.
A faulty PCV valve or clogged hose can cause a rough idle and poorly performing car. Check the system at least once a year and replace the valve every 20 months or 20,000 miles. A quick way to test the PCV valve is to free it from the grommet at the filler cap or valve cover and shake the valve. If the valve rattles it is probably all right.
If you own or can borrow an engine tachometer, a better way to test the PCV valve is as follows:
- Connect a tachometer to the engine.
- With the engine idling, remove the PCV valve from its mounting grommet.
- Check the tachometer reading. Place a finger over the valve. Suction should be felt.
- Check the tachometer reading again. The engine speed should have dropped at least 50 rpm. It should return to the first reading when the finger is removed from the opening.
- If the engine does not change speed or if the change is less than 50 rpm, the hose is clogged or the PCV valve is bad. Check the hose first, if it is not clogged replace the PCV valve.