Volkswagen Golf/Jetta/Cabriole 1990-1999

Positive Crankcase Ventilation System



The system consists of a tube from the air filter housing to the rocker/camshaft cover and a second tube from the rocker/camshaft cover to the intake manifold. Under normal operating conditions, clean air flows from the air filter into the rocker/camshaft cover where it mixes with crankcase oil vapors. These vapors are drawn through the PCV valve and into the intake manifold to be burned with the air/fuel mixture. The flow to the intake manifold is metered by the PCV valve. When manifold vacuum is high, the valve is pulled closed and flow is restricted to maintain a smooth idle. If crankcase pressure is very high, vapors can flow directly into the air filter housing.

A plugged PCV system will cause oil leaks or a build up of sludge in the engine. An air filter coated with engine oil indicates excessive crankcase pressure. A leaking valve or hose might cause rough or high idle, engine stalling and/or Powertrain Control Module (PCM) trouble codes.

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Fig. PCV system flow diagram

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Fig. Cutaway view of the PCV valve, allowing the flow of mixed air into the intake manifold


  1. Visually inspect the PCV valve hose, the fresh air supply hose and their attaching nipples or grommets for splits, cuts, damage, clogging, or restrictions. Repair or replace, as necessary.
  3. If the hoses pass inspection, start the engine and allow it to warm until normal operating temperature is reached.
  5. Remove the PCV valve from the rocker arm cover, but leave it connected to the hose. With the engine at idle, feel the end of the valve for manifold vacuum. If there is no vacuum, check for a plugged or leaking hose, PCV valve or manifold port. Replace a plugged or damaged hose.
  7. Stop the engine and remove the PCV valve. It should rattle when shaken. If the valve does not rattle or it is plugged, replace the valve.


PCV valve removal and installation is covered in Section 1. Refer to Section 1 for any maintenance regarding the PCV system.