Acura Coupes and Sedans 1994-2000 Repair Information

Crankcase Ventilation System



The Positive Crankcase Ventilation (PCV) system is used to control crankcase blow-by vapors. The gases are recycled in the following way:

As the engine is running, clean, filtered air is drawn through the air filter and into the crankcase. As the air passes through the crankcase, it picks up the combustion gases and carries them out of the crankcase, through the PCV valve, and into the induction system. As they enter the intake manifold, they are drawn into the combustion chamber where they are reburned.

The most critical component in the system is the PCV valve. This valve controls the amount of gases which are recycled into the combustion chamber. At low engine speeds, the valve is partially closed, limiting the flow of gases into the intake manifold. As engine speed increases, the valve opens to admit greater quantities of gases into the intake manifold. If the PCV valve becomes clogged, the system is designed to allow excessive amounts of blow-by gases to back flow through the crankcase tube into the air cleaner to be consumed by normal combustion.

The Positive Crankcase Ventilation (PCV) system must be operating correctly to provide complete removal of the crankcase vapors. Fresh air is supplied to the crankcase from the air filter, mixed with the internal exhaust gases, passed through the PCV valve and into the intake manifold.

The PCV valve meters the flow at a rate depending upon the manifold vacuum. If the manifold vacuum is high, the PCV restricts the flow to the intake manifold. If abnormal operating conditions occur, excessive amounts of internal exhaust gases back flow through the crankcase vent tube into the air filter to be burned by normal combustion.


Never operate an engine without a PCV valve or a ventilation system, except as directed by testing procedures, for it can become damaged.

Incorrect operation of the PCV system can cause multiple driveability symptoms.

A plugged valve or hose may cause:

Rough idle
Stalling or slow idle speed
Oil leaks
Sludge in engine

A leaking valve or hose would cause:

Rough idle
High idle speed

PCV Valve See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: Pulling the PCV valve from the intake manifold

  1. Remove the PCV valve from the intake manifold or valve cover.
  3. Run the engine at idle.
  5. Place your thumb over the end of the valve. Check for vacuum. If there is no vacuum at the valve, check for plugged valve or vacuum lines.
  7. Shut off the engine. Shake the valve and listen for the rattle. If valve doesn't rattle, replace it.

System Functional Check

  1. Check the crankcase ventilation valve for correct application.
  3. Run engine until normal operating temperature is obtained.
  5. Block off crankcase ventilation system fresh air intake passage.
  7. Remove the engine oil dipstick and install a vacuum gauge on the dipstick tube.
  9. Run the engine at 1500 rpm for 30 seconds, then read the vacuum gage while at 1500 rpm. If vacuum is present, the crankcase ventilation system is functioning properly. No vacuum indicates the engine may not be sealed and/or is drawing in outside air. Check valve cover and oil pan gaskets for leaks and repair, as required. If the vacuum gage registers a pressure or the vacuum gage is pushed out of the dipstick tube, check for the correct crankcase ventilation valve, a plugged hose or excessive engine blow-by.


Refer to General Information and Maintenance for removal and installation of the PCV valve. The PCV nipple should be replaced and inspected every 60,000 miles (96,000 km).